Remove double has_column check in new=>store_column

Standardize exception texts across ::Row
Consolidate bits and pieces under ::_Util::refdesc

No functional changes
Add one extra is_exception check (missed a spot during 841efcb3f)

In addition tweak the message so that carp_unique can in fact catch it
properly, and test that the proper amount of warnings is in fact emitted
(travis) T::B 1.005 is superseded by 1.300 - remove handholding
Skip the namespace tests on plain install

Protect users from future spurious changes in uncleaned imports
Move the "special loading" check to DBICTest::Util

No functional changes
(travis) Temporary hard-spec of the SQLA dep, lockstep release
is_X_value functions introduced in 3705e3b28 migrated to SQLA