use pure config mode.
we no longer compile a test application for the libraries,
however checks have been tightened by making sure version of
all opm modules are the same.
this allows for putting prereqs directly in the module repositories
- pass on toolchain file
- don't build examples in static directories
- allow non-install mode and custom targets in opm_from_git
- use origin/master to make sure static source trees are built from the
top should user re-execute the build in an existing build tree
