commandserver: get around ETIMEDOUT raised by selectors2
selector.select() should exits with an empty event list on timed out, but
selectors2 raises OSError if timeout expires while recovering from EINTR.
Spotted while debugging new chg feature.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..