ca-certificates: use c_rehash tool written in C

taken from
http://rt.openssl.org/Ticket/Display.html?id=3505&user=guest&pass=guest
written by Timo Teräs aka @fabled from alpine linux.

this makes it possible to switch from openssl to libressl and at the same
time getting rid of all perl dependencies in the openssl dependency chain
(the original c_rehash tool, required by ca-certificates and shipped with
openssl, but missing from libressl, was written in perl).

closes #90 (again).