fbset: fix mode matching code: original code may trigger false positive.

fbset: fix mode matching code: original code may trigger false positive.
 E.g. fbset -n '16bit'
 succeeded at 'mode "640x480 16bit"' and that is wrong.
 Also parser is rewritten. By Vladimir.

function                                             old     new   delta
static.syncs                                           -      20     +20
g_options                                              4       -      -4
g_cmdoptions                                         432     385     -47
fbset_main                                          1842    1642    -200