Add runtime and arch flags to use command

Previously, you had to use a full package name to select a coreclr based
runtime with dnvm use.  With this change we now support the -r and -a
flags line in powershell.  For example, the following all work:

 $ dnvm use 1.0.0-dev -r coreclr
 $ dnvm use 1.0.0-dev -r mono
 $ dnvm use 1.0.0-dev -r coreclr -a x64
 $ dnvm use 1.0.0-dev -r coreclr -a x86

For mono based runtimes we ignore the architecture if one is passed in
on the command line.  We defaut to x64 as an architecture for coreclr if
one is not set explicitly.

Author: ellismg

src/dnvm.sh

@@ -54,6 +54,16 @@ if [ -z "$DNX_FEED" ]; then
     DNX_FEED="$_DNVM_DEFAULT_FEED"
 fi
 
+__dnvm_current_os()
+{
+    local uname=$(uname)
+    if [[ $uname == "Darwin" ]]; then
+        echo "darwin"
+    else
+        echo "linux"
+    fi
+}
+
 __dnvm_find_latest() {
     local platform="mono"
 
@@ -188,23 +198,33 @@ __dnvm_unpack() {
 
 __dnvm_requested_version_or_alias() {
     local versionOrAlias="$1"
+    local runtime="$2"
+    local arch="$3"
     local runtimeBin=$(__dnvm_locate_runtime_bin_from_full_name "$versionOrAlias")
 
     # If the name specified is an existing package, just use it as is
     if [ -n "$runtimeBin" ]; then
         echo "$versionOrAlias"
     else
-       if [ -e "$_DNVM_ALIAS_DIR/$versionOrAlias.alias" ]; then
-           local runtimeFullName=$(cat "$_DNVM_ALIAS_DIR/$versionOrAlias.alias")
-           local pkgName=$(echo $runtimeFullName | sed "s/\([^.]*\).*/\1/")
-           local pkgVersion=$(echo $runtimeFullName | sed "s/[^.]*.\(.*\)/\1/")
-           local pkgPlatform=$(echo "$pkgName" | sed "s/$_DNVM_RUNTIME_PACKAGE_NAME-\([^.]*\).*/\1/")
+        if [ -e "$_DNVM_ALIAS_DIR/$versionOrAlias.alias" ]; then
+            local runtimeFullName=$(cat "$_DNVM_ALIAS_DIR/$versionOrAlias.alias")
+            echo "$runtimeFullName"
         else
             local pkgVersion=$versionOrAlias
-            local pkgPlatform="mono"
-        fi
 
-        echo "$_DNVM_RUNTIME_PACKAGE_NAME-$pkgPlatform.$pkgVersion"
+            if [[ -z $runtime || "$runtime" == "mono" ]]; then
+                echo "$_DNVM_RUNTIME_PACKAGE_NAME-mono.$pkgVersion"
+            elif [[ "$runtime" == "coreclr" ]]; then
+                local pkgArchitecture="x64"
+                local pkgSystem=$(__dnvm_current_os)
+
+                if [ "$arch" != "" ]; then
+                    local pkgArchitecture="$arch"
+                fi
+
+                echo "$_DNVM_RUNTIME_PACKAGE_NAME-coreclr-$pkgSystem-$pkgArchitecture.$pkgVersion"
+            fi
+        fi
     fi
 }
 
@@ -247,10 +267,12 @@ __dnvm_help() {
     echo ""
     echo "  adds $_DNVM_RUNTIME_SHORT_NAME bin to path of current command line"
     echo ""
-   printf "%b\n" "${Yel}$_DNVM_COMMAND_NAME use <semver>|<alias>|<package>|none [-p -persistent] ${RCol}"
+   printf "%b\n" "${Yel}$_DNVM_COMMAND_NAME use <semver>|<alias>|<package>|none [-p|-persistent] [-r|-runtime <runtime>] [-a|-arch <architecture>] ${RCol}"
     echo "  <semver>|<alias>|<package>  add $_DNVM_RUNTIME_SHORT_NAME bin to path of current command line   "
     echo "  none                        remove $_DNVM_RUNTIME_SHORT_NAME bin from path of current command line"
     echo "  -p|-persistent              set selected version as default"
+    echo "  -r|-runtime                 runtime to use (mono, coreclr)"
+    echo "  -a|-arch                    architecture to use (x64)"
     echo ""
    printf "%b\n" "${Yel}$_DNVM_COMMAND_NAME run <semver>|<alias> <args...> ${RCol}"
     echo "  <semver>|<alias>            the version or alias to run"
@@ -371,18 +393,30 @@ dnvm()
         ;;
 
         "use"|"run"|"exec" )
-            [[ $1 == "use" && $# -gt 3 ]] && __dnvm_help && return
             [[ $1 == "use" && $# -lt 2 ]] && __dnvm_help && return
+
             local cmd=$1
             local persistent=
+            local arch=
+            local runtime=
 
             shift
             if [ $cmd == "use" ]; then
+                local versionOrAlias=
                 while [ $# -ne 0 ]
                 do
                     if [[ $1 == "-p" || $1 == "-persistent" ]]; then
                         local persistent="true"
+                    elif [[ $1 == "-a" || $1 == "-arch" ]]; then
+                        local arch=$2
+                        shift
+                    elif [[ $1 == "-r" || $1 == "-runtime" ]]; then
+                        local runtime=$2
+                        shift
+                    elif [[ $1 == -* ]]; then
+                        echo "Invalid option $1" && __dnvm_help && return 1
                     elif [[ -n $1 ]]; then
+                        [[ -n $versionOrAlias ]] && echo "Invalid option $1" && __dnvm_help && return 1
                         local versionOrAlias=$1
                     fi
                     shift
@@ -404,7 +438,7 @@ dnvm()
                 return 0
             fi
 
-            local runtimeFullName=$(__dnvm_requested_version_or_alias "$versionOrAlias")
+            local runtimeFullName=$(__dnvm_requested_version_or_alias "$versionOrAlias" "$runtime" "$arch")
             local runtimeBin=$(__dnvm_locate_runtime_bin_from_full_name "$runtimeFullName")
 
             if [[ -z $runtimeBin ]]; then