check-config: mention the file and line of the error

I used this to more quickly track down a failing test-check-config.t issue
in another repo. I thought it might be useful more generally, so I'm sending
it out in case others think it's a worthwhile change.

contrib/check-config.py

@@ -48,7 +48,9 b' def main(args):'
         prevname = ''
         confsect = ''
         carryover = ''
+        linenum = 0
         for l in open(f):
+            linenum += 1
 
             # check topic-like bits
             m = re.match('\s*``(\S+)``', l)
@@ -110,9 +112,10 b' def main(args):'
                     default = '<variable>'
                 if (name in foundopts and (ctype, default) != foundopts[name]
                     and name not in allowinconsistent):
-                    print(l)
+                    print(l.rstrip())
                     print("conflict on %s: %r != %r" % (name, (ctype, default),
                                                         foundopts[name]))
+                    print("at %s:%d:" % (f, linenum))
                 foundopts[name] = (ctype, default)
                 carryover = ''
             else:

tests/test-check-config.t

@@ -32,8 +32,8 b' Sanity check check-config.py'
 
   $ $PYTHON contrib/check-config.py < $TESTTMP/files
   foo = ui.configint('ui', 'intdefault', default=42)
-  
   conflict on ui.intdefault: ('int', '42') != ('int', '1')
+  at $TESTTMP/testfile.py:12: (glob)
   undocumented: ui.doesnotexist (str)
   undocumented: ui.intdefault (int) [42]
   undocumented: ui.intdefault2 (int) [42]