chgserver: update the umask cache before each run
posix.py uses a global variable to store the umask value resulting in caching of
it when using chg. We need to update it before each command run as the umask can
change between commands.
This fixes test-inherit-mode.t with chg.
$ hg init
$ echo a > a
$ hg ci -Ama
adding a
$ hg an a
0: a
$ hg --config ui.strict=False an a
0: a
$ echo "[ui]" >> $HGRCPATH
$ echo "strict=True" >> $HGRCPATH
$ hg an a
hg: unknown command 'an'
(use 'hg help' for a list of commands)
[255]
$ hg annotate a
0: a
should succeed - up is an alias, not an abbreviation
$ hg up
0 files updated, 0 files merged, 0 files removed, 0 files unresolved