checknlink: return False if .hgtmp file preexists (issue2517)
If os_link fails on Windows, errno is always errno.EINVAL,
so we can't really say if the testlink could not be created
because (a) the FS doesn't support hardlinks or (b) there
is a leaked .hgtmp file lying around from a previous crashed
run.
So let's err on the safe side, keep the code simple and assume
we can't detect hardlinks in both cases.
$ hg init
$ echo a > a
$ hg ci -Am0
adding a
$ hg -q clone . foo
$ touch .hg/store/journal
$ echo foo > a
$ hg ci -Am0
abort: abandoned transaction found - run hg recover!
[255]
$ hg recover
rolling back interrupted transaction
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
Check that zero-size journals are correctly aborted:
$ hg bundle -qa repo.hg
$ chmod -w foo/.hg/store/00changelog.i
$ hg -R foo unbundle repo.hg
adding changesets
abort: Permission denied: $TESTTMP/foo/.hg/store/.00changelog.i-* (glob)
[255]
$ if test -f foo/.hg/store/journal; then echo 'journal exists :-('; fi