Remove # $FreeBSD$ from Makefiles.

math/R: Update to version 4.0.0

Upstream changes:
https://stat.ethz.ch/pipermail/r-announce/2020/000653.html

Also bump PORTREVISION of ports that depend on math/R.

Submitted by:	wen (in part)
Reviewed by:	jwb, Rainer Hurling <rhurlin@gwdg.de>, thierry
Differential Revision:	https://reviews.freebsd.org/D24572

Bump PORTREVISION for ports depending on the canonical version of GCC
as defined in Mk/bsd.default-versions.mk which has moved from GCC 8.3
to GCC 9.1 under most circumstances now after revision 507371.

This includes ports
 - with USE_GCC=yes or USE_GCC=any,
 - with USES=fortran,
 - using Mk/bsd.octave.mk which in turn features USES=fortran, and
 - with USES=compiler specifying openmp, nestedfct, c11, c++0x, c++11-lang,
   c++11-lib, c++14-lang, c++17-lang, or gcc-c++11-lib
plus, everything INDEX-11 shows with a dependency on lang/gcc9 now.

PR:		238330

- Update to 0.2.1

Bump PORTREVISION for ports depending on the canonical version of GCC
defined via Mk/bsd.default-versions.mk which has moved from GCC 7.4 t
GCC 8.2 under most circumstances.

This includes ports
 - with USE_GCC=yes or USE_GCC=any,
 - with USES=fortran,
 - using Mk/bsd.octave.mk which in turn features USES=fortran, and
 - with USES=compiler specifying openmp, nestedfct, c11, c++0x, c++11-lang,
   c++11-lib, c++14-lang, c++17-lang, or gcc-c++11-lib
plus, as a double check, everything INDEX-11 showed depending on lang/gcc7.

PR:		231590

Bump PORTREVISIONs of all users of math/mpc that we just updated to
version 1.1.0 (via revision 464079).

- Update to 0.2.0

assertthat is an extension to stopifnot() that makes it easy to
declare the pre and post conditions that you code should satisfy,
while also producing friendly error messages so that your users
know what they've done wrong.

WWW: https://cran.r-project.org/web/packages/assertthat/