To check importing modules in perf.py for historical portability, this
patch lists up files by "hg files" both for "1.2" and tip, and builds
up "module whitelist" check from those files.
This patch uses "1.2" as earlier side version of "module whitelist",
because "mercurial.error" module is a blocker for loading perf.py with
Mercurial earlier than 1.2, and just importing "mercurial.error"
separately isn't enough.
This patch introduces tests/check-perf-code.py as a preparation for
adding extra checks on contrib/perf.py in subsequent patches (mainly,
for historical portability).
At this change, check-perf-code.py doesn't add any extra check, and is
equal to check-code.py. This makes subsequent patch focus only on
adding an extra check on perf.py check-perf-code.py.
check-perf-code.py adds extra checks on perf.py by wrapping
contrib/check-code.py, because "filtering" by check-code.py (e.g.
normalize characters in string literal or comment line) is useful to
simplify regexp for check, and avoid false positive matching.
