Use explicit "SHELL=/usr/bin/env bash" in Makefile.in after all

...instead of "SHELL=@BASH@" from d3f7d05d
"Clean up OOO_SHELL" which could expand to SHELL=/bin/sh which, at least on
Mac OS X 10.7 with /usr/bin/make 3.81, could apparently lead to recipe lines
calling ooinstall being directly exec'ed from make and failing to find ooinstall
in solenv/bin, instead of going via the shell and taking into account PATH from
included config_host.mk.

Change-Id: I841dc30f72d1d8841c64f48408a669eb6a37a1f3

Makefile.in

@@ -13,7 +13,7 @@ ifeq ($(MAKECMDGOALS),)
 MAKECMDGOALS:=all
 endif
 
-SHELL=@BASH@
+SHELL=/usr/bin/env bash
 SRCDIR := @SRC_ROOT@
 BUILDDIR := @BUILDDIR@