Document KCM ccache type

Document the new KCM ccache type in ccache_def.rst.  Document the
kcm_socket and kcm_mach_service variables in krb5_conf.rst.

https://github.com/krb5/krb5/commit/4ac345865276e8848546ba75e09feecc23e8a040
Author: Greg Hudson <ghudson@mit.edu>
Commit: 4ac345865276e8848546ba75e09feecc23e8a040
Branch: master
 doc/admin/conf_files/krb5_conf.rst |   13 +++++++++++++
 doc/basic/ccache_def.rst           |   21 ++++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)