krb5_cc_gen_new

[Sam Hartman]

The Linux linker complains about the use of mktemp in
src/lib/krb5/ccache/cc_file.c.

I don't think mktemp is used unsafely in that instance.  However I'm
wondering whether krb5_cc_gen_new is ever used.

In particular, looking at the code, it seems that you would end up
with a ccache of the form /tmp/tktxxxxxx.  I suspect that would
confuse those of us who are familiar with krb4 ticket files.

I propose to change tkt_root to /tmp/krb5cc_ and to use mkstemp
instead of tempnam when available in the interests of avoiding linker
warnings that might cause p.people to believe we have security
problems.