VL (with Jared): add scopestack abstraction for looking up various kinds of things, and use that in various transforms
Merge branch 'master' into scopestack
vl -- porting more transforms to use scopestacks
scopestack work
more work on scopestacks
fix up a few remaining things broken by scopestack stuff
fix more breakage
VL: Add tools for looking up variables, definitions, etc. in nested
namespaces (mlib/scopestack.lisp).  Change some existing transforms to
use them.