Implemented a 'sasl' auth_type for better control over authentication
flow specific to SASL.
Implemented 'sasl_dn_regex' and 'sasl_dn_replacement' config variables
for mapping from a SASL authentication ID to a bind DN, a necessary step
when using GSSAPI/Kerberos where there is no explicit bind DN provided.
Fixed setting of Kerberos credentials cache location in environment
variable. The location is derived from either an already set
environement variable or the SERVER variable set by the Apache
mod_auth_kerb module.
See http://modauthkerb.sourceforge.net/configure.html
