Merge branch 'configure_no_wrf' into develop (PR #175)

Merge branch 'configure_no_wrf' into develop (PR #175)

This merge adds a new option, --nowrf, to the configure script so that the WPS
can be configured without a compiled WRF model.

Only three of the WPS components -- geogrid, metgrid, and int2nc -- require
the WRF I/O libraries. Even if none of these components was needed, it was
previously still necessary to either compile WRF or to make manual changes to
the configure script.

This merge introduces logic in the configure script to check for a command-
line argument, --nowrf, that, if present, disables checks in the configure
script for a compiled WRF directory. This enables, for example, the compilation
of the ungrib program without needing to compile the WRF model.

* configure_no_wrf:
  Add --nowrf option to configure script, for configuring without WRF