hg-cpython: fallback when encountering an unknown matcher
At this point in the process, nothing user-visible has happened, it is still
safe to fallback. This can happen now that we're going to be using
"container matchers" like unionmatcher and intersectionmatcher.
This is easier and less error-prone than recursive checking beforehand since
only the presence of a transformation case will allow the process to continue.
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present