ident->name in middle
undo cowardly hiding of eq-check

I've reversed my thinking on this restrictive definition of eq after
two separate bugs were hidden by commenting it out; it's better to
get ICEs than SIGSEGV's, any day.

RE-ENABLING ICE MACHINE!
added run-pass test for issue #9049
auto merge of #9090 : jbclements/rust/let-var-hygiene, r=luqmana

This appears to fix issue #9049. It also re-enables the ICE check on comparing idents for equality; it appears that ICEs are better than seg faults.