hgweb: catch util.Abort raised by addchangegroup Right now, if a pretxnchangegroup hook fails, we send some HTML error message to the client and the transaction is not rolled back (issue499). Catching util.Abort allows us to send a decent message to the client and for some reason makes the rollback complete. This patch is not perfect since it doesn't fix the reason why the transaction wasn't rolled back (maybe some circular references?). Also, the transaction is aborted only after we've sent the response back to the client and the "transaction aborted" message ends up in the logs of the web server.

1 files updated, 0 files merged, 0 files removed, 0 files unresolved
pulling from ../source
abort: pretxncommit hook exited with status 1
transaction abort!
rollback completed
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
(run 'hg update' to get a working copy)
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 2 changesets, 2 total revisions