Fixes for UIOP:RUN-PROGRAM on ACL.
On ACL, the :INPUT and :OUTPUT arguments to EXCL:RUN-SHELL-COMMAND take NIL for the behavior of inheriting input and output handles from the Lisp process. These were encoded as T in UIOP:RUN-PROGRAM, instead of NIL, causing ACL to get errors trying to open T as a file designator. Added a couple of test cases to test-run-program.script to illustrate the problem. Note that this fix does not provide the prescribed behavior for :OUTPUT NIL (which should take the program's output and throw it on the floor). There is a TODO in uiop:run-program explaining what's missing. In brief, ACL's EXCL:RUN-SHELL-COMMAND does not support this behavior out of the box, so one would have to capture the program's output, and then throw it on the floor.
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