[Indic] Track base position when reordering things

Ouch, how did things ever work without this?!  The added test that has a
dot-reph as well as a pre-base reordering Ra perfectly demonstrates the
bug (tested with Nirmala font from Win8 for example).  Testing suggests
that Win8 shaper has the *exact* same bug / behavior that we used to
have.  Odd.
2 files changed