[SSSD] [PATCHES] Support native IPA netgroups

[Jan Zelený]

I'm sending couple patches which add support for IPA netgroups:

#53
These routines were not static, so I renamed them in order to avoid confusion 
and possible collision with equivalent routines in IPA provider

#54
Some new config options, please focus on this patch, I'm not entirely sure if 
my approach was the correct one.

#55
This new context was necessary so I can pass ipa options to routine 
determining host search base.

#56
This is netgroups support itself

#57
IPA id provider which is utilizing previously added support of netgroup 
fetching

Thanks
Jan