RFC/weak symbols status ignore

Fix fortran 2008 when OpenMPI is configure'd with --disable-weak-symbols.

this was initially introduced in http://www.open-mpi.org/community/lists/devel/2014/09/15774.php

a simpler but suboptimal workaround can be provided for the v1.8 branch if this one is too big.

This fixes the failure of the following tests from the ibm test suite (except many_to_one) reported at
http://mtt.open-mpi.org/index.php?do_redir=2212

this PR has a simple conflict with PR #228 and i will fix it when/if #228 lands into the master

@jsquyres could you please review this ?