util: move checkosfilename call from path_auditor to opener
path_auditor is used for checking patterns too, but a pattern is not a valid
filename.
This patch fixes
98ee3dd5bab4, which introduced the bug:
$ hg log -l3 glob:**.py
abort: filename contains '*', which is reserved on Windows: mercurial\**.py
grep: don't print data from binary files for matches (
issue2614)