fix B02004 and other projectile related killer reasons

fix B02004 and other projectile related killer reasons

1) killer reason for scattered land mine shrapnel used "a" or "an" prefix
   even when multiple projectiles hit as a group -- one of various things
   From a bug report.oextra field) --
   noticed while investigating #1 and later From a bug report.4.0 due to an unintentional side-effect of missile killer reason
   handling in 3.4.1 (removal of redundant "poisoned" prefix by m_throw()
   confused the poison handling routine) -- noticed while investigating #3.