contacts: update CLT dependency
skalibs 1.5.1 (new formula)

A set of general-purpose C programming libraries.
execline 1.3.1 (new formula)

A small scripting language, to be used in place of a shell in
non-interactive scripts.
s6 1.1.3 (new formula)

skarnet.org's small & secure supervision software suite.
skalibs: add 1.5.1 bottle.
execline: add 1.3.1 bottle.
s6: add 1.1.3 bottle.