Major rewrite of depends_t(), added GET_ALL to dict.h, filesys.h revised

depends_t() now can handle multiple "libs" search paths, [however, it
is necessary to re-fix the directory shadowing problem]. In addition,
get_all was added to dict.h, which returns all values matching a key.
Many changes were made to filesys.h, such as fixing path_eq(), adding
path_is_rel() (determines if path is relative), rel_is_within() and
rel_get_within() [further explanation in comments to come]
because I'd be interrupted to write a .gitignore...