Fix hang when dropping content needs to lock the content on a ssh remote,
which occurred when the remote has git-annex version 5.20151019 or newer.
Analysis: `race` runs 2 threads at once, and the hGetLine finishes first.
So, it tries to cancel the waitForProcess, but unfortunately that is making
a foreign call and so cannot be canceled. The remote git-annex-shell
is waiting for a line on stdin before it will exit. Deadlock.
This only occurred sometimes; I reproduced it going from darkstar to
elephant, but not from darkstar to darkstar. Not sure how that fits into
the above analysis -- perhaps a race condition is also involved?
Fixed by not using `race`; now the hGetLine will fail with an exception
if the remote git-annex-shell exits without any output.
Made all Annex.Perms file mode changing functions ignore errors when
core.sharedRepository is set, because the file might be owned by someone
else. I don't fancy getting bug reports about crashes due to set modes in
this configuration, which is a very foot-shooty configuration in the first
place.
The fsck warning is necessary because old repos kept files mode 444, which
doesn't allow locking them, and so if the mode remains 444 due to the file
being owned by someone else, the user should be told about it.
When annex.thin is set, adding an object will add the execute bits to the
work tree file, and this does mean that the annex object file ends up
executable.
This doesn't add any complexity that wasn't already present, because git
annex add of an executable file has always ingested it so that the annex
object ends up executable.
But, since an annex object file can be executable or not, when populating
an unlocked file from one, the executable bit is always added or removed
to match the mode of the pointer file.
