Fixed external builder "make WALA.CAst" to run properly
(by default it is disabled.)
One needs to set workspace variable $bash to point to
a bash executable (with explicit ".exe" suffix on Windows)
git-svn-id: https://wala.svn.sourceforge.net/svnroot/wala/trunk@941 f5eafffb-2e1d-0410-98e4-8ec43c5233c4