tests: introduce check-perf-code.py to add extra checks on perf.py 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.