py3: make keys of keyword arguments strings

keys of keyword arguments on Python 3 has to be string. We are dealing with
bytes in our codebase so the keys are also bytes. Done that using
pycompat.strkwargs().

Also after this patch, `hg version` now runs on Python 3.5. Hurray!

mercurial/dispatch.py

@@ -803,7 +803,8 b' def _dispatch(req):'
 
         msg = ' '.join(' ' in a and repr(a) or a for a in fullargs)
         ui.log("command", '%s\n', msg)
-        d = lambda: util.checksignature(func)(ui, *args, **cmdoptions)
+        strcmdopt = pycompat.strkwargs(cmdoptions)
+        d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
         try:
             return runcommand(lui, repo, cmd, fullargs, ui, options, d,
                               cmdpats, cmdoptions)

tests/test-check-py3-commands.t

@@ -9,6 +9,6 b' The full traceback is hidden to have a s'
   >   $PYTHON3 `which hg` $cmd 2>&1 2>&1 | tail -1
   > done
   version
-  TypeError: Can't convert 'bytes' object to str implicitly
+  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   debuginstall
   TypeError: Can't convert 'bytes' object to str implicitly