gdb on MacOS X does not seem to be very fond of "flat" dSYM files, but
it can read the bundle variant fine. Thus we change that to enable
debugging across several tools.
As of 2013-09 the DUNE code that reads dune.module is not MultiArch-
aware. Thus, for a 64-bit platform it will look in lib/ on Debian and
lib64/ on RHEL.
dune.module does not contain any paths to architecture-specific
binaries. It is therefore always installed in no-arch lib/ directory.
Thus, there is no need to have a variable for this, and there was
no other users of this variable either.
If the option USE_VERSIONED_DIR is set to ON (default is OFF), then
most files are installed in a ${suite}-${label}/ subdirectory
(e.g. header files go in "/usr/include/opm-2013.03/"). This enables
us to easily install backports of newer versions on systems which
have a system package for an older one, without getting conflicts.