Making the next_free_pair_object and next_free_single_object as inline functions.
Also contains a patch from Wolfgang with changes to the instantiation file.

Background: In release mode, GNU-4.8.x (OSX) seem to optimize away the calls when
specializing the template functions and then symbol definitions seem to be different
between debug and optimized modes. This causes undefined linkage for release mode.

References:
[1] https://groups.google.com/forum/#!topic/dealii/c2qjAsuJ7Mc
[2] https://code.google.com/p/dealii/issues/detail?id=137
[3] https://groups.google.com/forum/#!msg/dealii/6RXRR-iac0Y/Tjzwg1rFRMQJ
Merge pull request #192 from vijaysm/vijaysm/tria_objects_release_fix

Making next_free_pair_object and next_free_single_object as inline functions
Remove explicit instantiations.

Since these functions were moved to the header file, we no longer
need to explicitly instantiate them since every .cc file that uses
them will generate an instantiation where necessary.
Merge pull request #193 from bangerth/omit-explicit-instantiations

Remove explicit instantiations.
Check in DoFHandler::renumber_dofs() that DoFs are distributed

- This adds several Asserts to check that DoFs are distributed
before calling renumber_dofs() for active or level DoFs.
- Note that we now also require that you call distribute_dofs()
before distribute_mg_dofs().
- Updated documentation.
Merge pull request #191 from tjhei/renumber_dofs_asserts

Check in DoFHandler::renumber_dofs() that DoFs are distributed
Remove Assert in CellAccessor::face()

The Assert checked that DoFs are distributed before allowing the use of
::face(), which is overly restrictive.

Also see https://groups.google.com/d/topic/dealii/G3Xp-Uv72_M/discussion
Merge pull request #194 from tjhei/remove_face_it_assert

Remove Assert in CellAccessor::face()