Make IsPathSection treat sections that end in certain trailing characters such as ! (exclude lists) as path sections.
Make IsPathSection treat sections that end in certain trailing characters such
as ! (exclude lists) as path sections.

BUG=gyp 138
TEST=none
Review URL: http://codereview.chromium.org/599011
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google