Update manifest-versions logic to check whether version number needs to be bumped.
Update manifest-versions logic to check whether version number needs to be bumped.

BUG=chromium-os:24764
TEST=unit tests, pylint

Change-Id: I892a455578a9360205b7007f1f0334c5767ba378
Reviewed-on: https://gerrit.chromium.org/gerrit/13969
Reviewed-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

coreos/chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,zhang0137/chromite,chadversary/chromiumos.chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,zhang0137/chromite,chadversary/chromiumos.chromite