remotefilelog: fix various minor py3 problems
# skip-blame b prefixes and pycompat.long, nothing remotely interesting
Differential Revision: https://phab.mercurial-scm.org/D5223
ui: wrap whole _write() block with timeblockedsection
I think the cost of color labeling is negligible compared to the I/O
syscalls. Let's simply wrap the whole write() function so that we can
eliminate _write() and _write_err() in later changeset.