Support references in convert_to_*

Support references in convert_to_*

conver_to_* functions now accept REFERENCE values, which will be
unwrapped before performing the usual conversion. This is consistent
with convert_scalar_to_number and matches the expected behavior in
a couple random use-sites I checked.

Also includes a couple fixes/cleanups elsewhere and two tests for
cases that previously didn't work (though the reference issue existed
all over the place).