revlog: resolve lfs rawtext to vanilla rawtext before applying delta
This happens when a LFS delta base gets a non-LFS delta from another client.
In that case, the LFS delta base needs to be converted to non-LFS version
before applying the delta.
Differential Revision: https://phab.mercurial-scm.org/D2069
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors