configure changes

[Carson Gaspar]

Once again, I will state what the _correct_ logic for finding libraries 
should be (and what my old patch implemented):

If --with-pkg=/path/to/pkg was passed, look for lib in /path/to/pkg/lib 
(using /path/to/pkg/include). If it's not there, give up. If found, prepend 
path to LDFLAGS and CPPFLAGS.

If an explicit path was _not_ given, try, in order:

- The system defaults (i.e. do _not_ add any -L/-R/-I flags). If found, 
great - no paths needed. If not found, try next.
- A list of default directories (which should be settable on a per-OS 
basis). The simple default list is /usr/local. If found, append path to 
LDFLAGS and CPPFLAGS. If not found, give up.

Things to note carefully in the above:

- Explicit paths are _prepended_, implicit paths are _appended_
- If explicit paths are specified for everything, implicit paths are 
_never_ used.

-- 
Carson