check-code: discard filtering result of previous check for independence

Before this patch, check-code.py applies filtering on the file
content, to which filtering of previous check is already applied.

This might hide issues, which should be detected by a subsequent check
in "checks" list.

Fortunately, this problem hasn't appeared, because there is no
overlapping of filename matching (examined in the order below).

  1. *.py or *.cgi
  2. test-* (not *.t suffix)
  3. *.c or *.h
  4. *.t
  5. *.txt
  6. *.tmpl

For example, adding a test, which wants to examine raw comment text in
*.py files, at the end of current "checks" list doesn't work as
expected, because a filter for *.py files normalizes comment text in
them.

Putting such test at the beginning of "checks" list also resolves this
problem, but such dependence on the order decreases maintainability of
check-code.py itself.

This patch discards filtering result of previous check at the
beginning of each checks, for independence of each checks.

contrib/check-code.py

@@ -537,6 +537,7 b' def checkfile(f, logfunc=_defaultlogger.'
         return result
 
     for name, match, magic, filters, pats in checks:
+        post = pre # discard filtering result of previous check
         if debug:
             print(name, f)
         fc = 0