check-py3-compat: manually format and print warnings...
check-py3-compat: manually format and print warnings
The warnings mechanism may print to stderr on Python 3. Independent buffering
of stdout and stderr can lead to warnings output not being printed properly.
This commit traps warnings when executing individual files and prints
warnings to stdout so output is deterministic.
Differential Revision:
https://phab.mercurial-scm.org/D5845
