* module/system/il/ghil.scm (ghil-lookup): So, it turns out this function
needed to be split into three:
(ghil-var-is-bound?, ghil-var-for-ref!, ghil-var-for-set!): The
different facets of ghil-lookup. Amply commented in the source. The
difference being that we now allocate variables that are set! on the
heap, so that other continuations see their possibly-modified values.
(force-heap-allocation!): New helper.
* testsuite/Makefile.am:
* testsuite/t-call-cc.scm: New test, that variables that are set! are
allocated on the heap, so that subsequent modifications are still
seen by the continuation. The test was distilled from test 7.3 in
r5rs_pitfall.test.
