Call ninja with relative paths.

Calling the ninja script with absolute paths under cygwin would pass
posix-style paths, and would cause errors since ninja would force
calling itself under cmd.exe, which uses Windows-style paths.
Support running update script from cygwin.
Make apply-patches compatible with python 2.6.

Chromium ships binary of python 2.6 instead of 2.7.
Fix indent.
Treat cygwin platform as win32.
Checks Popen's return code.
Return "returncode" in main function instead of calling exit.
Mention we are using standard win32 python in comment.
PLATFORM => TARGET_PLATFORM.
Merge pull request #17 from brightray/cygwin

Support building libchromiumcontent under cygwin