tests/test-bad-extension.t

caches: invalidate store caches when lock is taken

The fncache was not being properly invalidated each time the lock was taken, so
in theory it could contain old data from prior to the caller having the lock.
This changes it to be invalidated as soon as the lock is taken (same as all our
other caches).

  $ echo 'raise Exception("bit bucket overflow")' > badext.py
  $ abspath=`pwd`/badext.py

  $ echo '[extensions]' >> $HGRCPATH
  $ echo "gpg =" >> $HGRCPATH
  $ echo "hgext.gpg =" >> $HGRCPATH
  $ echo "badext = $abspath" >> $HGRCPATH
  $ echo "badext2 =" >> $HGRCPATH

  $ hg -q help help
  *** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
  *** failed to import extension badext2: No module named badext2
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