Add a --snapshot option for revinfo.  If set, revinfo prints a .gclient file set to sync to the current revisions/hashes on disk
Add a --snapshot option for revinfo.  If set, revinfo prints a .gclient file
set to sync to the current revisions/hashes on disk

Add a --gclientfile=FILENAME option.  If set, gclient loads FILENAME
rather than .gclient for configuration info.

Patch contributed by jneddo@nvidia.com

BUG=1658
TEST=Verify that --snapshot prints a valid configuration file
     Verify that when --gclientfile is set the correct file is used
     Verify that gclient sync --gclientfile sets the correct revisions

Review URL: http://codereview.chromium.org/672004

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@41078 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

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