Solving/Simplifying the RPATH or INSTALL_DIR

Created by: anjos

Currently, to build our Ubuntu or OSX packages, we need to disable the setting of these variables as files get moved during installation using debuild or MacPorts. Here is a strategy to get rid of this annoyance:

1. Move the library _core_array.so to the <prefix>/lib directory and version it properly
2. Make all other python bindings depend on that instead of a library hidden at python directories
3. Make the python bindings use the RPATH by default (this is disabled when the user passes -DCMAKE_SKIP_BUILD_RPATH=TRUE to CMake. Under OSX, have a similar mechanism that will do that for the INSTALL_DIR property.

Notes:

1. The RPATH functionality is only required for the python bindings
2. The python bindings only require that functionality if the libraries they depend on are not installed in a standard location.