lang/python{27,33,34,35,36}: Make Python curses module work with Unicode

Use readline from ports (USES= readline:port) and patch
setup.py to ignore readline from base. The patch is necessary for
FreeBSD < 1100000, as after this the readline library became an
INTERNALLIB, see base r268461 [1]

Link devel/readline against termcapw instead of termcap is part of
this change, see ports r444463 [2]

Note that this is the ports approach for getting Python curses
module working with Unicode. The other way is splitting libncurses
into separate libncurses and libtinfo in base, for which an open
issue exists [3].

Apart from Python language ports, at least www/rtv and
sysutils/py-ranger ports have been tested to work correctly
(display Unicode) after this change.

[1] https://svnweb.freebsd.org/changeset/base/268461
[2] https://svnweb.freebsd.org/changeset/ports/444463
[3] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197317

PR: 171246, 197317
Reported by: Vitaly Magerya <vmagerya gmail com>
Reviewed by: garga, koobs, miwi, sunpoet
Approved by: garga (mentor), sunpoet (python, with hat)
Differential Revision: https://reviews.freebsd.org/D11127