ui: also swap sys.stdout with self.fout in _readline
In
17ffb30d9174, _readline was changed to output a space using
raw_input and this was done using sys.stdout directly, not self.fout.
This change broke the command server for JavaHg since it (and other
clients) would see a spurious ' ' on stdout and interpret this as an
unknown channel.
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda