Add rcache feature to gss_acquire_cred_from

The "rcache" cred store entry can specify a replay cache type and name
to be used with the credentials being acquired.

[ghudson@mit.edu: split up, simplified, and altered to fit preparatory
commits]

https://github.com/krb5/krb5/commit/7dad0bee30fbbde8cfc0eacd2d1487c198a004a1
Author: Simo Sorce <simo@redhat.com>
Committer: Greg Hudson <ghudson@mit.edu>
Commit: 7dad0bee30fbbde8cfc0eacd2d1487c198a004a1
Branch: master
 src/lib/gssapi/krb5/acquire_cred.c |   48 ++++++++++++++++++++++++++---------
 src/lib/gssapi/krb5/gssapiP_krb5.h |    1 +
 2 files changed, 36 insertions(+), 13 deletions(-)