Created by: toshipiazza
If instrument_post_write and instrument_mem both reserve the same
register via drreg, drreg may elide a register save and restore in
between them. If the application instruction relies on this particular
register as well, drutil_insert_get_mem_addr will also compute the
address incorrecly.
We fix this by restoring the app register explicitly.
Fixes #2449 (closed)