contrib: check reference to old selenic.com domain

Now, all URL in Mercurial source tree should refer mercurial-scm.org
domain instead of selenic.com.

*.po files are ignored in this patch, because they might contain
msgid/msgstr coming from old source files.

This ignorance seems safe enough, because such msgstr should be
ignored at runtime, because:

  - msgid corresponded to it should be invalid, or
  - msgstr itself should be marked as fuzzy at synchronized to recent hg.pot

If any additional examination for *.po files is needed in the future,
let i18n/check-translation.py achieve such examination.

BTW, some binary files (e.g. *.png) are meaningless for checking
reference to old domain in this patch, but aren't ignored like as *.po
files, because excluding multiple suffixes is difficult for regexp
matching.

contrib/check-code.py

@@ -444,6 +444,17 b' webtemplatepats = ['
   ]
 ]
 
+allfilesfilters = []
+
+allfilespats = [
+  [
+    (r'(http|https)://[a-zA-Z0-9./]*selenic.com/',
+     'use mercurial-scm.org domain URL'),
+  ],
+  # warnings
+  [],
+]
+
 checks = [
     ('python', r'.*\.(py|cgi)$', r'^#!.*python', pyfilters, pypats),
     ('test script', r'(.*/)?test-[^.~]*$', '', testfilters, testpats),
@@ -456,6 +467,8 b' checks = ['
     ('txt', r'.*\.txt$', '', txtfilters, txtpats),
     ('web template', r'mercurial/templates/.*\.tmpl', '',
      webtemplatefilters, webtemplatepats),
+    ('all except for .po', r'.*(?<!\.po)$', '',
+     allfilesfilters, allfilespats),
 ]
 
 def _preparepats():