krb5_parse_name not thread-safe, not responsive to environment changes

krb5_parse_name not thread-safe, not responsive to environment changes

As Ezra noted, krb5_parse_name saves away the default realm the first
time it looks it up, and will never look it up again, even if the
config file has changed, the context isn't the same one, etc.  It also
used a static variable which wasn't thread-safe.

With this patch, we still won't catch changes in the config file
specification after the default realm has been looked up for a given
krb5_context, because it's cached in the context too, but this will at
least be more responsive, and thread safe.

* parse.c (krb5_parse_name): Don't cache the default realm name.

ticket: new
target_version: 1.4
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@16988 dc483132-0cff-0310-8789-dd5450dbe970