tests: New test-suite-only command __cmd

tests: New test-suite-only command __cmd

Adding or removing a command to/from a test has unfortunate effects:

* Before the previous commit: if the command consumes pseudorandom
  numbers, all subsequent users of pseudorandom numbers get different
  ones.  This has always been a major headache.

* Since the previous commit: all subsequent users of pseudorandom
  numbers get different ones whether the command consumes any or not.
  That's even worse.

* If the command uses BTUs, subsequent prompts are changed.  Not
  nearly as bad as the above, but still annoying.

Create a new command __cmd to allow compensating for adding/removing
commands for tests.  Throw in the ability to compensate treasury
changes for good measure.  Three arguments: command count, BTU use,
money use.

Usage example: say you add a convert command to a test, and it uses 3
BTUs and $15.  Then you compensate by adding "__cmd added 1 3 15"
right after it.

The command must not be available unless running_test_suite is on, of
course.  Make it require the new player command capability TESTING,
and give that to all players when running_test_suite is on.

The command is intentionally not documented in info.  Switch
running_test_suite off for info-test, to hide it (and any future
TESTING commands) from info-test.

Suppress the command counter increment for TESTING commands, so they
can be used without upsetting pseudorandom numbers

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>