[CM] Error compiling CM on Ubuntu Feisty Fawn with SBCL and CMUCL

[Tobias Kunze Briseño]

IIRC, cm.sh had to be made to lie about being bash because OSX
used to provide bash as /bin/sh and did NOT provide a /bin/bash.
And, since none of the target platforms would actually run a bash
provided as /bin/sh in such a strict "sh" mode as to break the
script, the kludge worked for us at that time (2001?).  Of
course, that broke it for someone who was running it on an Alpha,
but then we found out that this person was using his own script
anyway.

The real problem, of course, is that cm.sh has always been a bash
script that should be ported to plain sh.  But if all platforms
provide /bin/bash now, then maybe that's no longer an issue.

-t