use and propagate DESTDIR as appropriate
DESTDIR support for library search and packlist
don't need to update packlist if packlist is turned off
use subtests for readability; rmtree for directories

unlink doesn't do anything to a directory / folder on most platforms
so use rmtree.  This is probably overkill anyway since the directories
shouldn't exist if the test passes
correct document hierarchy
test for DESTDIR
s/grep/map/

also the /e is unnecessary in this case
extra commentary
Merge pull request #65 from plicease/destdir

DESTDIR support