Add tests for krb5_sname_match()

(back ported from commit 83dae972736d823216c20dd559e30c7d41361289)

https://github.com/krb5/krb5/commit/1939b23ad293d3bcb525d1821b461915ac997ed0
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 1939b23ad293d3bcb525d1821b461915ac997ed0
Branch: krb5-1.13
 .gitignore                       |    1 +
 src/lib/krb5/krb/Makefile.in     |   11 +++-
 src/lib/krb5/krb/t_sname_match.c |  117 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 127 insertions(+), 2 deletions(-)