Testing requirements amendment

Hi,

I havea minor suggestion for http://llvm.org/docs/TestingGuide.html:

Under 'Requirements', might be worth mentioning that running the basic llvm/clang regression tests (check-all) requires a version of bash that supports pipefail, i.e. bash 3.0+. On older system where /bin/sh is too old, one simply needs to hack LitConfig.py to point to /somewhere/else/bash that meets this requirement.
(This method has been tested on powerpc-darwin8.)

Thanks!

Fang

I would prefer a patch to make lit fail in an understandable way if it
detects an incompatible version of bash; if someone sees a test
failing, the version of bash isn't going to be high on the list of
things to check.

-Eli