calc 2.12.6.4 release

The following are the changes in this release:

Fixed a man page warning about ./myfile where the leading dot
was mistook for an nroff macro.  Thanks goes to David Haller
<dnh at opensuse dot org> for providing the patch.

Improved gen_v1(h,n) in lucas.cal for cases where h is not a
multiple of 3. Optimized the search for v(1) when h is a
multiple of 3.

Fixed a Makefile problem, reported by Doug Hays <doughays6 at gmail
dot com>, where if a macOS user set BINDIR, LIBDIR, CALC_SHAREDIR
or INCDIR in the top section, their values will be overwritten by
the Darwin specific section.