Config code updates.

CONF_modules_unload() now calls CONF_modules_finish()
automatically.

Default use of section openssl_conf moved to
CONF_modules_load()

Load config file in several openssl utilities.

Most utilities now load modules from the config file,
though in a few (such as version) this isn't done
because it couldn't be used for anything.

In the case of ca and req the config file used is
the same as the utility itself: that is the -config
command line option can be used to specify an
alternative file.