Log Message:
cad/oce: fixes for Darwin

Currently cad/oce does not build on Darwin, in part because sed
substitutions in CMakeFiles fail because the suffixes (.dylib) differ
from expected (.so).  There are, however, two additional problems.
First, frameworks are not used by pkgsrc, yet CMakeLists.txt expects
them on Darwin and uses special installation steps.  Instead, use the
standard installation steps.  Additionally, there are a few PLIST
differences between Darwin and other platforms, which are handled with
PLIST.* variables that differentiate Darwin from other systems.