mod_auth_mellon large scale interoperability.

Issue

Current version of mod_auth_mellon in RHEL 6.6 (0.8.0) suffers from few problems
not allowing us to deploy it at large organization scale:

1.) The generated apache session environment size is limited to 128 elements
(env. variables): in our MS ADFS environment that number of elements can be
as high as 1024 (user groups) - current implementation of mod_auth_mellon
exits with 'internal server error' in such case.

[ `https://github.com/UNINETT/mod_auth_mellon/issues/10` ]

2.) related to 1.) - by default generated environment contains series of
variables named alike MYVAR_0=val0 , MYVAR_1=val1 .. etc (single values).
This is not very practical for programmatic comparisons .. (and makes
porting of in-house applications from other auth. providers complicated)
Multivalue variables alike MYVAR=val0;val1;... etc as for example
shibboleth/mod_shib generates seem to be more suitable for that purpose.

[  `https://github.com/UNINETT/mod_auth_mellon/pull/9` ]

3.) a bug: MellonCond does not work with MellonSetEnv(NoPrefix)

[ `https://github.com/UNINETT/mod_auth_mellon/issues/12` ]