Port dart:io Path tests to package:path.

pkg/path/README.md

Index: pkg/path/README.md
diff --git a/pkg/path/README.md b/pkg/path/README.md
index dacacaa8396c66c6027eba754b9611c1d9f8cb51..bbc78a44a7186cba150f14410b423ddc24792993 100644
--- a/pkg/path/README.md
+++ b/pkg/path/README.md
@@ -73,6 +73,16 @@ Trailing separators are ignored.
 
     builder.dirname('path/to/'); // -> 'path'
 
+If an absolute path contains no directories, only a root, then the root
+is returned.
+
+    path.dirname('/');    // -> '/' (posix)
+    path.dirname('c:\');  // -> 'c:\' (windows)
+
+If a relative path has no directories, then '.' is returned.

[Bob Nystrom, 2013/07/15 17:49:29]

You'll want a blank line after this. Markdown needs blank lines before and after
code blocks.

[Bill Hesse, 2013/07/16 12:42:26]

Done.

+    path.dirname('foo');  // -> '.'
+    path.dirname('');     // -> '.'
+

[Bob Nystrom, 2013/07/15 17:49:29]

I like this.

 ### String extension(String path)
 
 Gets the file extension of [path]: the portion of [basename] from the last