write: add the possibility to pass keyword argument from batchget to vfs
We are going to pass atomictemp keyword argument from merge.baychget to
vfs.__call__. Update all the frames to accept **kwargs and pass it to the next
function.
Differential Revision: https://phab.mercurial-scm.org/D1881
#require docutils gettext
$ $TESTDIR/check-gendoc zh_CN
checking for parse errors