mq: avoid silent failure when single patch doesn't apply (issue4604) The error-handling here is quite byzantine. self._apply raises an AbortNoCleanup, but self.apply was swallowing the exception and returns 2. In self.push, we catch all exceptions.. and cleanup. We try to print a message to clean up.. but that relies on having a top-of-stack. Instead, we re-raise the abort in self.apply, and avoid cleanup on AbortNoCleanup in self.push by adding a trivial new except clause. We also modernize the now-visible abort message.

pushkey: flush pending data before running a pre-pushkey hook (issue4607) The pre-pushkey hook will likely validate the pushkey based on element previously changed in the same transaction. We need to make theses data available for the hook.

pushkey: use hook arguments from transaction when one exists When pushkey is called during a transaction, we include its 'hookargs' when running the pre-pushkey hooks. Having more data cannot hurt, especially the transaction ID.

util.h: also sniff for C99 before trying to use stdbool.h (issue4605) stdbool.h isn't required until C99. Sigh.