manual: Mark perror as MT-unsafe and update check-safety.shHEADmaster

The manual marked perror as MT-safe, but then listed a remark
indicating that it was unsafe because of a race between the function
and access to stderr.  The function is indeed MT-unsafe because
of the unlocked access to stderr internals and bug 32730 has been
filed to address this issue.

The script manual/check-safety.sh should have caught this issue,
but a missed escaping of "?" along with searching of all inputs
again via "$@" resulted in a non-functional regexp.

In order to avoid regressions we also update check-safety.sh.

The script manual/check-safety.sh is updated in the following ways:

 * The MT-unsafe remarks in MT-safe context check is fixed.
   - It now detects the perror safety note mistake.

 * Comments updated indicating that we allow MT context marks
   to count for other contexts if they are related.
   - This is why commit ad9c4c536115ba38be3e63592a632709ec8209b4
     failed and the failure is now understood as expected.

 * All checks now have verbose output.

 * Back reference based duplicate checks are removed.
   - They are too complex and don't cover all cases.

No regressions on x86_64.

0 files changed, 0 insertions, 0 deletions