BASH is defined when you are actually using bash during configure, which
sucks because it ends up being '/bin/sh', messing up all of our scripts.
Change the name of the variable we use in configure, and also ensure we get
a full path to the executable by using AC_PATH_PROGS rather than
AC_CHECK_PROGS. Finally, change the variable name everywhere we use it.
Signed-off-by: Dan McGee <dan@archlinux.org>
6eedf06fcc