[krbdev.mit.edu #5583] support include in the profile library

[Public Submitter via RT]

Adding support for file and (particularly) directory inclusion (where
the latter includes every non-dotfile in the directory) to the profile
library would be very useful for easier management of krb5.conf.  Among
the benefits:

Distributions could ship standard krb5.conf files with reasonable
defaults and a collection of public realms, and then local
administrators could drop in their own files as needed without changing
the default file.

The KDC and kadmind configuration could be kept in a separate file so
that all hosts can use the same krb5.conf file even if one doesn't want
to put KDC data into the default krb5.conf.

Other software that uses the appdefaults section for its own
configuration information (Kerberos PAM modules, for example) could drop
in a separate configuration file without modifying the system krb5.conf.