Fix Trac #1755; check for stage errors in TH quoted Names

Fix Trac #1755; check for stage errors in TH quoted Names

There are a number of situations in which you aren't allowed to use
a quoted Name in a TH program, such as
	\x -> 'x
But we weren't checking for that!  Now we are.

Merge to stable branch.

Test is TH_qname.