Fix the swig build on Windows (broken since r926613) and use a simpler  construct to check a prefix.
Fix the swig build on Windows (broken since r926613) and use a simpler 
construct to check a prefix.

* build/generator/gen_win.py
  (get_proj_sources): Add description to swig custom build operations
  (get_proj_sources): Use .startswith() instead of a range check.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@930042 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion