[krbdev.mit.edu #8566] krb5_init_context() should detect set-uid-ness

[Greg Hudson via RT]

I am a bit concerned that using the broken issetugid() on FreeBSD (and 
NetBSD, if it's also broken there) could break legitimate uses of 
Kerberos environment variables with httpd.  Of course we can address 
that, at least partially, by limiting our use of issetugid() to 
platforms where it is known not to be broken.