check-commit: try to fix multiline handling
The old code did not understand the difference between the first line of the summary,
and a random line in the summary that happened to include a #, or a
random line in the changes that happened to include it.
965788d9ae09 is an example where it fails
check-commit: support REVs as commandline arguments
usage:
* HG_NODE=REV check-commit
* hg export REV | check-commit
* check-commit REV ...