Fix support for Visual Studio 2010 Express projects.

Use the proper version string, and omit the folder mappings section for
2010 Express.

Patch by jmadill@chromium.org!

BUG=376
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/27685004

git-svn-id: http://gyp.googlecode.com/svn/trunk@1767 78cadc50-ecff-11dd-a971-7dbc132099af