Miscellaneous corrections to RST docs

Fix various small errors pointed out by Ben Kaduk (and a couple of
minor misstatements in text adjacent to them).

https://github.com/krb5/krb5/commit/302ae137d14ce848046040934ff48a8e673771f0
Commit By: ghudson
Revision: 25769
Changed Files:
U   trunk/doc/rst_source/krb_admins/realm_config.rst
U   trunk/doc/rst_source/krb_users/tkt_mgmt.rst