convert: add parseclosemap method This is a copy of the parsesplicemap method and will serve as a way to specify which changesets to close while converting.

convert: add mapname parameter to checkrevformat Upcoming patches will add new map files so we change the calling sequence of checkrevformat so that error messages will let the user know which file has the wrong rev format.

convert: replace old sha1s in the description This is a simple find-and-replace strategy for matching anything in the old description of a converted commit and, if that matched sha1 exists in the mapping, replacing it with the new sha1. In particular, this is helpful for descriptions that contain tags with messages such as, "Added tag 1.0 for commit abcde1234567" which will now be automatically converted. Tests have been updated accordingly.