Read GSS configuration files with mtime 0

There is at least one case (with flatpaks) where configuration files
in the special read-only /etc all have an mtime of 0.  Using an
initial last modified time of 0 in g_initialize.c causes these files
to never be read.

Change the initial high value to the be the "invalid" value
(time_t)-1.  Since the C and POSIX standards do not require time_t to
be signed, special-case the checks in load_if_changed() and
updateMechList() to treat all mod times as newer than -1.

[ghudson@mit.edu: edited commit message; slightly modified approach]

https://github.com/krb5/krb5/commit/2b34a007461065e0cab4490dfe1ae5ddd10da67b
Author: Simo Sorce <simo@redhat.com>
Committer: Greg Hudson <ghudson@mit.edu>
Commit: 2b34a007461065e0cab4490dfe1ae5ddd10da67b
Branch: master
 src/lib/gssapi/mechglue/g_initialize.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)