Speedups round 2

    map::has_flag*(...): optional usage of bitfield constants, for flags checked
    heavily enough to create a noticable performance bottleneck ( ie "BASHABLE"
    and most anything used in update_scent, monster movement, los & drawing,
    vehicles, fire, etc)

    map move_cost & flag functions: eliminate redundant inbound and nonant calcs
     for ter + fun checks. still no clue what 'nonant' means

    monmove sanity & speedup
    * monster::sees_player( int & ): same as game::sees_u( x, y, int & ) but
    eliminates expensive and silly logic of monster::plan passing position
    to game::sees_u, which proceeds to do a keypair lookup in _active_monsters
    for the monster's mem addr.
    * Constify const functions required to make sees_player const
    * game::sees_u: same as before, but defer to critter.sees_player which handles
    the same checks via citter.vision and g->u.is_invisible
    * monster::plan use in-class sees_player which bypasses the whole 'this = map[ this.pos() ]'
      stuff partially responsible for it's 30% chunk of do_turn