Fix misdirected nuclear detonation output

Fix misdirected nuclear detonation output

Output went to the owner of the nuke instead of the player.
Fortunately, they're the same in normal usage.  They can differ only
when a deity drops a foreign nuke from a foreign plane.

The fix also cleans up a misuse of mpr() in kaboom(): it used multiple
calls to print a single line, which creates a separate bulletin for
each part.  The read command normally merges the bulletins, but if the
bulletins are more than five seconds apart (clock jumped somehow), we
get a bulletin header in the middle of a line.  Fortunately, that
could happen only when a deity drops a foreign nuke.  Before commit
a269cdd7 (v4.3.23), it could also happen for missions.

Broken in Empire 2.