tests: execute check-config.py without xargs

Before this patch, test-check-config.t fails on Solaris, because
"xargs" doesn't invoke check-config.py with all filenames at once.

"xargs" may invoke specified command multiple times with part of
arguments given from stdin: according to "xargs(1)" man page, this
dividing arguments is system-dependent.

For portability of test-check-config.t, this patch adds "xargs" like
mode to check-config.py and executes it in test-check-config.t without
"xargs".

contrib/check-config.py

@@ -105,4 +105,7 b' def main(args):'
                 print "undocumented: %s (%s)%s" % (name, ctype, default)
 
 if __name__ == "__main__":
+    if len(sys.argv) > 1:
     sys.exit(main(sys.argv[1:]))
+    else:
+        sys.exit(main([l.rstrip() for l in sys.stdin]))

tests/test-check-config.t

@@ -5,4 +5,4 b''
 New errors are not allowed. Warnings are strongly discouraged.
 
   $ hg files "set:(**.py or **.txt) - tests/**" | sed 's|\\|/|g' |
-  >   xargs python contrib/check-config.py
+  >   python contrib/check-config.py