understand failing tests for:
* OS X: test-rpath_merge.atf:rpath_merge
* NetBSD 4/5: ?

write better descriptions for:
* all tests

write tests for:
* WRAPPER_UPDATE_CACHE: but this is an optimization we won't be
    needing
* WRAPPER_REORDER_CMDS: test reordering when there is some, test
    that none happens when there isn't any
* _WRAP_TRANSFORM_CMDS: make sure _USE_RPATH is respected and that
    nothing else makes no-rpath happen
* WRAPPER_TRANSFORM_CMDS: test every type of transform individually;
    then test them together, combinatorially
* _WRAP_PATH: make sure WRAPPER_BINDIR ain't in it, and/or make
    sure whatever's being found when calling "gcc" (or whatever)
    ain't a wrapper
* WRAPPEES: test that the default list of wrappers makes all the
    right ones; test that adding a WRAPPEE makes it happen
* _WRAPPER_UNIQUE_CMDS: wtf is this doing? stripping WRAPPEES so
    _WRAPPEES has no duplicates? what's a duplicate, exactly?
* _WRAP_ALIASES: make sure that these generate the right aliases
    and they have the right targets
* "strip the leading paths from the toolchain variables": hm? path
    test like the others?
* XXX all other current behaviors, whether we like them or not