Check that the getenv function exists too

Closes #178

//cc @vlucas, @GabeMedrash, @sfolador

Author: GrahamCampbell

src/Loader.php

@@ -337,7 +337,7 @@ public function setEnvironmentVariable($name, $value = null)
 
         // If PHP is running as an Apache module and an existing
         // Apache environment variable exists, overwrite it
-        if (function_exists('apache_setenv') && apache_getenv($name)) {
+        if (function_exists('apache_getenv') && function_exists('apache_setenv') && apache_getenv($name)) {
             apache_setenv($name, $value);
         }