There were three flags, WF_STRAIGHT, WF_THIN_SPREAD and WF_WIDE_SPREAD,
when only one flag, WF_SPREAD suffices. This makes the code simpler and
gets rid of some duplication.
Put the maximum amount of rockets that can be caried in the description, and
also adjust the amount of rocket pods one has when buying a secondary weapon.
The laser and charge beam will remove all rocket capacity. To soften the blow,
you get at least capacity for 5 rockets when buying homing missile systems,
or 10 when buying normal missile system.