Ensure that all entries in .sln files are sorted.
Ensure that all entries in .sln files are sorted.

Previously this the NestedProjects section was sorted
according to dictionary key ordering which resulted
in differing sln files between gyp runs.

BUG=http://code.google.com/p/gyp/issues/detail?id=296

Review URL: https://chromiumcodereview.appspot.com/10943017

csulmone/gyp,csulmone/gyp,csulmone/gyp,csulmone/gyp