refrain from forcing a hardwired SHELL value, cf. 1494ded298a6 but it becomes obsolete again in 549969a7f582 and follow-ups;
--- a/src/Pure/IsaMakefile Fri May 21 16:49:33 2010 +0200
+++ b/src/Pure/IsaMakefile Fri May 21 17:26:42 2010 +0200
@@ -12,8 +12,6 @@
## global settings
-SHELL = /bin/bash
-
SRC = $(ISABELLE_HOME)/src
OUT = $(ISABELLE_OUTPUT)
LOG = $(OUT)/log