Now enforces ChangeInfo.issue (and .patchset) to be a int.
Renamed LoadChangelistInfo() to ChangeInfo.Load().
Removed ChangeInfo.__init__() default parameters.

TEST=none
BUG=none

Review URL: http://codereview.chromium.org/118355

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@17836 0039d316-1c4b-4281-b951-d872f2087c98