Corrected documentation for gnutls_x509_trust_list_add_trust_*
gnutls_x509_trust_list_remove_cas() and derivatives will utilize a black list.

When a CA or certificate is removed from the trusted list, it is also
added in a blacklist to ensure that it will not be accepted due to
interdependency (e.g., it is a subordinate CA), or because it is not a CA.

Conflicts:
	lib/x509/verify-high.c
Added configure option --with-default-blacklist-file

This option allows to specify a file containing blacklisted certificates.

Conflicts:
	lib/system.c
backported makefile for doc generation
doc update
doc update