Inspired by the dirstate fix in 39954a8760cd, this should fix any race
conditions with the fsmonitor state changing from underneath.
Since we now grab the wlock for any non-invalidate writes, the only situation
this appears to happen in is with a concurrent invalidation. Test that.
fsmonitor could write out bad state if interrupted part way through, and
would then crash when it tried to read it back in.
Make both sides of the operation more robust - reading state should fail
cleanly, and we can use atomictemp to write out cleanly as the file is
small. Between the two, we shouldn't crash with an IndexError any more.
Since (b) is banned, we should do the same for (a) for consistency.
a) from mercurial import hg
from mercurial.i18n import _
b) from . import hg
from .i18n import _
Extension to plug into a Watchman daemon, speeding up hg status calls by
relying on OS events to tell us what files have changed.
Originally developed at https://bitbucket.org/facebook/hgwatchman
