Fix name-capture bug in rule matching

The matching algorithm for RULES should respect alpha-conversion, but it
wasn't doing so.  In particular, if the names of the template variables
clashed with a variable in scope at the call site, bad things could happen
(it showed up as a CoreLint failure when compiling nofib/real/parser)

This patch fixes the problem; see Note [Template binders]

Test is in simplCore/should_compile/spec002, but nofib -O2 in
	real/parser, real/fulsom