Fix SvnInfo to handle a non-svn workspace: can't deduce the version 
available, but it won't stop the build either.

Patch by: mike.aizatsky
Review by: fabbott



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@3717 8db76d5a-ed1c-0410-87a9-c151d255dfc7