Description of problem:
Semanage export always uses a (add) even in cases where -m (-modify) needs to be used (modifying record specified in policy).
Reproducible for "semange login" and "semanage fcontext" (and maybe others).

Version-Release number of selected component (if applicable):
policycoreutils-

Steps to Reproduce:

1. semanage login -m -s unconfined_u -r s0-s0:c0.c1023 _default_
2. semanage export -f /tmp/exp
3. semanage login -D
4. semanage import -f /tmp/exp
   ValueError: Login mapping for _default_ is already defined

Alternative reproducer:

1. semanage fcontext -m -t boot_t "/xen(/.*)?"
2. semanage export -f /tmp/exp
3. semanage fcontext -D
4. semanage import -f /tmp/exp
   ValueError: File context for /xen(/.*)? already defined

Actual results:
The login/fcontext mapping gets removed by semanage import.

Expected results:
The login/fcontext mapping is removed and re-add by semanage import (semanage login -D, semanage login -m -s unconfined_u -r s0-s0:c0.c1023 _default_).