When the WITH_TCLTK option is turned on at config-time, use the
bsd.tcl.mk API. Although this changes Tcl version from 8.4 to 8.5
for most Tcl-users, there is no PORTREVISION bump, because TCLTK
option is off by default.
While here, slightly rephrase the descriptions of the two SSL-options
(GNUTLS vs. NSS).
Approved by: maintainer