maint: revert premature merge of pull request #23.

Reverse apply 5508adb.
maint: move GNU make only rules to GNUmakefile.

* Makefile.am (SPECL_OPTS, specl_verbose_, specl_verbose_0)
(specl_verbose_1): Move from here...
* GNUmakefile: ...to here.
(specl_verbose_1): Now that Specl-3 passes --verbose on to the
selected formatter to handle, explicitly request the long-form
report formatter for `make check V=1`.