post-receive: exclude commits from the patch update step

post-receive: exclude commits from the patch update step

When merging upstream work related to other projects into your own
project repository, you probably don't want to check for (and try to
update) the status on every change-set in the merge. So add a list of
references (branches, tags, commits, etc.) whose commits should be
ignored in the patch update step.

This could be used, for example, to set:

    EXCLUDE="refs/heads/upstream"

Then when you're ready to merge in new upstream code, you first update
the 'upstream' branch before pushing your own.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>