Add test and fix bugs with multiple token-pasting on the same line.

Add test and fix bugs with multiple token-pasting on the same line.

The list replacement when token pasting was broken, (failing to
properly update the list's tail pointer). Also, memory management when
pasting was broken, (modifying the original token's string which would
cause problems with multiple calls to a macro which pasted a literal
string). We didn't catch this with previous tests because they only
pasted argument values.