tags: validate nodes in _getfnodes() and update cache in case of unknown nodes
`hgtagsfnodescache` can contain unknown nodes due to cache corruption and this
lead to a traceback on operations like `hg tags` as we don't validate nodes.
This patch validates that all filenodes returned after `hgtagsfnodescache` are
known to the repository. If there exists any unknown filenode, we force
recompute it and update the cache.
The test change demonstrates the fix.
Differential Revision: https://phab.mercurial-scm.org/D10083
#require no-windows
#testcases safe normal
#if safe
$ echo "[format]" >> $HGRCPATH
$ echo "exp-share-safe = True" >> $HGRCPATH
#endif
$ . "$TESTDIR/remotefilelog-library.sh"
$ cat >> $HGRCPATH <<EOF
> [extensions]
> remotefilelog=
> share=
> EOF
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ cd ..
$ hgcloneshallow ssh://user@dummy/master source --noupdate -q
$ hg share source dest
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R dest unshare