Removed RAD_CHECK entry in Perl, protomed RAD_CONFIG

RAD_CONFIG used to be an undocumented read-only clone of RAD_CHECK,
where RAD_CHECK was named incorrectly. Remove the RAD_CHECK, make
RAD_CONFIG read/write.

This should not be merged to 3.0.x, as it breaks backwards
compatibility.
Merge pull request #715 from qnet-herwin/perl_remove_rad_config

Removed RAD_CONFIG entry in Perl