util: fix the check for non-C99 compilers (issue4605)

histedit: fix rollup prompting for a commit message (issue4606) Commit 090da03361c5 broke histedit's rollup by causing it to open the editor. Turns out I missed a spot where the rollup option was read. This fixes that and adjusts the test to catch this case.

test-hook.t: don't directly use redirect to /dev/null in hook for Windows This goes with 57f1dbc99631. External hooks are run in cmd.exe, which doesn't know about /dev/null, but sh can handle it.

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.