Work around Linux session keyring write behavior

If the session keyring matches the user session keyring, write
explicitly to the user session keyring.  Otherwise the kernel might
create a new session keyring for the process, making the resulting
cache collection invisible to other processes.

(cherry picked from commit 0642afa544b00054048775d0b9796923bf018e22)

https://github.com/krb5/krb5/commit/dd9975a4345447f3e764472c4d14fb56fdeeece5
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: dd9975a4345447f3e764472c4d14fb56fdeeece5
Branch: krb5-1.12
 src/lib/krb5/ccache/cc_keyring.c |   28 ++++++++++++++++++++++++----
 1 files changed, 24 insertions(+), 4 deletions(-)