options: change -v parsing

options: change -v parsing

Handle -v flags as a special case in command line preparsing stage,
and change the option entry into a dummy one. Specifying "v" in config
file no longer works (and the dummy entry shows an error in this
case); "msglevel" can still be used for that purpose. Because the flag
is now interpreted at an earlier parsing stage, it now affects the
printing of some early messages that were only affected by the
MPLAYER_VERBOSE environment variable before.

The main motivation for this change is to get rid of the last
CONF_TYPE_FUNC option.