Merge PR icsharpcode#325: Ability to mimic a zip file created by a Linux file-system

* respect the VersionMadeBy property of ZipEntry
* correctly set HostSystem without clearing version

Author: bjorg

src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs

@@ -526,7 +526,7 @@ public int HostSystem
 
 			set
 			{
-				versionMadeBy &= 0xff;
+				versionMadeBy &= 0x00ff;
 				versionMadeBy |= (ushort)((value & 0xff) << 8);
 			}
 		}

src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs

@@ -428,7 +428,7 @@ public ZipFile(string name)
 		public ZipFile(FileStream file) :
 			this(file, false)
 		{
-			
+
 		}
 
 		/// <summary>
@@ -489,7 +489,7 @@ public ZipFile(FileStream file, bool leaveOpen)
 		public ZipFile(Stream stream) :
 			this(stream, false)
 		{
-			
+
 		}
 
 		/// <summary>
@@ -2157,7 +2157,7 @@ private int WriteCentralDirectoryHeader(ZipEntry entry)
 			WriteLEInt(ZipConstants.CentralHeaderSignature);
 
 			// Version made by
-			WriteLEShort(ZipConstants.VersionMadeBy);
+			WriteLEShort((entry.HostSystem << 8) | entry.VersionMadeBy);
 
 			// Version required to extract
 			WriteLEShort(entry.Version);

src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs

@@ -750,7 +750,7 @@ public override void Finish()
 			foreach (ZipEntry entry in entries)
 			{
 				WriteLeInt(ZipConstants.CentralHeaderSignature);
-				WriteLeShort(ZipConstants.VersionMadeBy);
+				WriteLeShort((entry.HostSystem << 8) | entry.VersionMadeBy);
 				WriteLeShort(entry.Version);
 				WriteLeShort(entry.Flags);
 				WriteLeShort((short)entry.CompressionMethodForHeader);