import-checker: loop to get list of locally defined modules at first

This is a preparation for subsequent patches, which expect that all
locally defined (= mercurial specific) modules are already known
before examinations.

Looping twice for specified modules is a little redundant, but
reasonable cost for improvement in subsequent patches.

contrib/import-checker.py

@@ -221,11 +221,14 b' def main(argv):'
     if argv[1] == '-':
         argv = argv[:1]
         argv.extend(l.rstrip() for l in sys.stdin.readlines())
+    localmods = {}
     used_imports = {}
     any_errors = False
     for source_path in argv[1:]:
+        modname = dotted_name_of_path(source_path, trimpure=True)
+        localmods[modname] = source_path
+    for modname, source_path in sorted(localmods.iteritems()):
         f = open(source_path)
-        modname = dotted_name_of_path(source_path, trimpure=True)
         src = f.read()
         used_imports[modname] = sorted(
             imported_modules(src, ignore_nested=True))