Load -t certificates before dropping privileges

Load the certificates from the directory given by -t into the
certificate cache after preinit, but before dropping privileges.  This
fixes a number of issues, such as -t directory not being found after
chroot()ing to a different root, -t directory inaccessible due to
changing user with -u, and when using encrypted keys.  This bug was
introduced in 0675219 as a spurious part of fixing #5.

Issue:		#20, #19
Reported by:	Miroslav Stampar