Gun rebalance. All pistols have force/maxvel 25k, muskets 50k

See GH #5 and http://www.bay12forums.com/smf/index.php?topic=125628.msg4760039#msg4760039 .

I'm not sure if this is a great solution or not; 50k may bump maximum
velocity speeds in DF, so this may not have any gameplay change at all. On the
other hand, this could result in muskets being overpowered. Testing would be
lovely.