Added CoreFoundation bundle plugin support

Added CoreFoundation bundle plugin support

Added CoreFoundation bundle plugin support to support library bundle plugin
code.  Also modified plugin types so they allocate a list of pointers rather
than a list of structs so that we can reuse the code that generates the
pointer types.  (Basically now krb5int_open_plugin_dir() can call
krb5int_open_plugin() rather than doing nearly the same thing.)

ticket: new
target_version: 1.5

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@17950 dc483132-0cff-0310-8789-dd5450dbe970