Adding libmesh_common.C for a place to hold the macro functions.

Adding libMesh::MacroFunctions::here().
Automake junk associated with adding a new file.
The libmesh_stop macro is now converted to a function.

This allows us to remove <unistd.h> from libmesh_common.h
Factoring out common parts of macros.

The macros:
* libmesh_error
* libmesh_error_msg
* libmesh_not_implemented
* libmesh_not_implemented_msg
* libmesh_file_error
* libmesh_file_error_msg

now use libMesh::MacroFunctions::report_error() internally.

This allows us to remove the the print_trace.h dependency from
libmesh_common.h
Removing csignal dependence from libmesh_common.h