gex: enhance format-patch to support commit list
gex: enhance format-patch to support commit list

support a commit list to define which commit need to be exported for
each Git repo, instead of by specifing a revision range

the commit list has a simple format:
* text start with "#" regarded as comment
* text end with ":" regarded as Git repo for the following commits
* one commit id for each line with ordered

joez/ptk,joez/ptk,joez/ptk