Properly resolve merge conflict between
5e9ed4a4665751becc865dcd800fcd533875a0e1 and
f60745e3e5a464539ba184082c1dcd8fc20d1270 (the variables have now been
moved to within OS specific conditions so that they can be resolved
correctly on each platform.)
Provide somewhat sane defaults for OCI_INCLUDE_DIR and OCI_LIB_DIR
(oracle instant client directories) on windows.
Add detailed instructions for installing the oracle instant client,
including notes about the default directories that the binding.gyp
looking for.