check-code: examine magic pattern matching against contents of a file

Before this patch, check-code examines "magic" pattern (e.g.
'^#!.*python') matching against not contents of a file, but name of
it.

This unintentionally omits code checking against Python source file,
of which filename doesn't end with "*.py" or "*.cgi", even though
contents of it starts with "#!/bin/python" or so.

In this change, 'pre' refers contents of file 'f'.

contrib/check-code.py

@@ -485,7 +485,7 b' def checkfile(f, logfunc=_defaultlogger.'
         if debug:
             print name, f
         fc = 0
-        if not (re.match(match, f) or (magic and re.search(magic, f))):
+        if not (re.match(match, f) or (magic and re.search(magic, pre))):
             if debug:
                 print "Skipping %s for %s it doesn't match %s" % (
                        name, match, f)