Remove extra '/' when findShortestPath $from is a directory

src/Composer/Util/Filesystem.php

@@ -316,7 +316,7 @@ class Filesystem
         $to = lcfirst($this->normalizePath($to));
 
         if ($directories) {
-            $from .= '/dummy_file';
+            $from .= $this->isDirectory($from) ? 'dummy_file' : '/dummy_file';
         }
 
         if (dirname($from) === dirname($to)) {
@@ -461,6 +461,17 @@ class Filesystem
         return (bool) preg_match('{^(file://|/|[a-z]:[\\\\/]|\.\.[\\\\/]|[a-z0-9_.-]+[\\\\/])}i', $path);
     }
     
+    /**
+     * Return if the given path is a directory
+     *
+     * @param  string $path
+     * @return bool
+     */
+    public static function isDirectory($path)
+    {
+        return substr($path, -1) === '/';
+    }
+
     public static function getPlatformPath($path)
     {
         if (defined('PHP_WINDOWS_VERSION_BUILD')) {

tests/Composer/Test/Util/FilesystemTest.php

@@ -112,6 +112,7 @@ class FilesystemTest extends TestCase
             array('/foo/bar_vendor', '/foo/bar', '../bar', true),
             array('/foo/bar_vendor', '/foo/bar/src', '../bar/src', true),
             array('/foo/bar_vendor/src2', '/foo/bar/src/lib', '../../bar/src/lib', true),
+            array('C:/', 'C:/foo/bar/', "foo/bar", true),
         );
     }