Clean up rcache if GSS krb5 acquire_cred fails

The error handler in acquire_cred_context didn't release the rcache,
which would cause it to leak if we failed after acquire_accept_cred.

(cherry picked from commit 9df0c4bdce6b88a01af51e4bbb9a365db00256d5)

https://github.com/krb5/krb5/commit/08b5facdaa3397126b7502d5b1cd1aff1216c840
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 08b5facdaa3397126b7502d5b1cd1aff1216c840
Branch: krb5-1.11
 src/lib/gssapi/krb5/acquire_cred.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)