store: optimze _auxencode() a bit by grouping the reserved names by length
This reduces perffncacheencode wall time on Windows 7 x64 for my netbeans clone
here from 4.3 to 4.0 (7% faster).
$ "$TESTDIR/hghave" inotify || exit 80
$ hg init
$ echo "[extensions]" > .hg/hgrc
$ echo "inotify=" >> .hg/hgrc
$ hg inserve -d --pid-file .hg/inotify.pid
$ echo a > a
$ hg ci -Aqm0
$ hg co -q null
$ hg co -q
$ hg st
$ cat a
a
$ kill `cat .hg/inotify.pid`