py3: use pycompat.byteskwargs() to convert opts to bytes We have converted opts to unicodes before passing them.

test-check-code: do not use xargs We have too many files, and passing them via arguments could cause strange errors on some platforms [1]. Since check-code.py can now take "-" and read file names from stdin, use it instead of xargs to avoid the argv size limit. [1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/096346.html

check-code: use "-" to specify a list of files from stdin This will be used by the next patch.