Findewoms.cmake: fix typo

it's 'start.hh', not 'start.h'...
Catch up to opm-material reorganisation.

Specifically, file <opm/material/constants.hh> was renamed to
<opm/material/Constants.hpp> and this renaming must be reflected in
the CMake probes for opm-material.
Use dSYM bundles as debugging containers (on MacOS X)

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.
Merge pull request #41 from bska/041_cmake

Synchronise build system with opm-core to restore debugging on MacOS X