way the resulting binaries have a better change of running on 10.3.

This patch also updates the search logic for sleepycat db3/4, without this
patch you cannot use a sleepycat build with a non-standard prefix; with this
you can (at least on OSX) if you add the prefix to CPPFLAGS/LDFLAGS at
configure-time. This change is needed to build the binary installer for OSX.