tripe.h: Make job index be unsigned int, not unsigned short.

tripe.h: Make job index be unsigned int, not unsigned short.

This is mainly (a) because we don't actually save space by using a
short, and (b) because it shuts up a compiler warning.

The warning is annoying.  The compiler complains that it has proven that
an assertion is always true.  Of course, it's nice when it can prove my
assertions, but they're /meant/ to be provably true!

This particular instance is particularly annoying, since it's only
/trivially/ true in the sense the compiler is warning about as a result
of a coincidence of data-type ranges, which may not hold on other
architectures -- on which the assertion is nontrivial but still
important.

Duh.