slib: update to 3.2.6.

slib-3b6 is a maintenance release with some new functions.  Details at
<http://cvs.savannah.gnu.org/viewvc/*checkout*/slib/slib/ChangeLog>

* comlist.scm (butnth): Added.
* guile-2.init: patch from
https://gist.github.com/alexgian/1fe75b0c3fc95cb46baae2f50ae9211c
* grapheps.scm (set-font): Fixed pointsize dependent scaling.
* Makefile (INSTALL_INFO): ginstall-info -> install-info.
* iso8601.scm (iso-8601->time): Use gmktime rather than mktime.
* mkclrnam.scm (load-rgb-txt): Make encoding case insensitive in
method m5x (FED-STD-595C1).
* Makefile, iso8601.scm, mklibcat.scm, slib.texi:
Added feature iso-8601: ISO 8601 Representation of dates and times.

(wiz)