Mudprog driver had strong bias in "random" pick.

The mudprog_driver function to pick a random player as a target in a
room had a very strong statistical bias in favor of the first chosen
victim. The routine has now been corrected to do a proper random pick.
Revert "Mudprog driver had strong bias in "random" pick."

This reverts commit 47ae6e9c9f668fdb8a1bcbec87d96652cff2774a.
Revert "Revert "Mudprog driver had strong bias in "random" pick.""

This reverts commit 52c6729619ed12195fec8094058ba65cd4d8133b.
GitHub, y u do dis to me?

Click a wrong button, suddenly 4 commits for one lousy change. Ugh.