Ticket History #6737: Trace logging

Add trace logging infrastructure code, enabled by the KRB5_TRACE
environment variable or the API functions krb5_set_trace_callback()
or krb5_set_trace_filename(). As a start, add tracing events for:
* AS-REQ client code, including FAST and preauth
* TGS-REQ client code
* AP-REQ and AP-REP code (client and server)
* sendto_kdc
* Selected ccache operations
* Selected keytab operations


https://github.com/krb5/krb5/commit/caa480251ebdebbc5c9093223267cf5634493b03
Commit By: ghudson
Revision: 24118
Changed Files:
U trunk/src/include/cm.h
U trunk/src/include/k5-int.h
A trunk/src/include/k5-trace.h
U trunk/src/include/krb5/krb5.hin
U trunk/src/lib/krb5/ccache/ccbase.c
U trunk/src/lib/krb5/ccache/ccfns.c
U trunk/src/lib/krb5/error_tables/krb5_err.et
U trunk/src/lib/krb5/keytab/ktfns.c
U trunk/src/lib/krb5/krb/fast.c
U trunk/src/lib/krb5/krb/gc_via_tkt.c
U trunk/src/lib/krb5/krb/get_creds.c
U trunk/src/lib/krb5/krb/get_in_tkt.c
U trunk/src/lib/krb5/krb/gic_pwd.c
U trunk/src/lib/krb5/krb/init_ctx.c
U trunk/src/lib/krb5/krb/mk_rep.c
U trunk/src/lib/krb5/krb/mk_req_ext.c
U trunk/src/lib/krb5/krb/preauth2.c
U trunk/src/lib/krb5/krb/rd_rep.c
U trunk/src/lib/krb5/krb/rd_req_dec.c
U trunk/src/lib/krb5/krb/send_tgs.c
U trunk/src/lib/krb5/libkrb5.exports
U trunk/src/lib/krb5/os/Makefile.in
U trunk/src/lib/krb5/os/sendto_kdc.c
A trunk/src/lib/krb5/os/trace.c