ipsec: Allow the shell in the shebang to be changed.

src/ipsec/Makefile.am

@@ -10,6 +10,7 @@ ipsec.8 : ipsec.8.in
 
 ipsec : ipsec.in
 	sed \
+	-e "s:@IPSEC_SHELL@:/bin/sh:" \
 	-e "s:@IPSEC_VERSION@:$(PACKAGE_VERSION):" \
 	-e "s:@IPSEC_NAME@:$(PACKAGE_NAME):" \
 	-e "s:@IPSEC_DISTRO@::" \

src/ipsec/ipsec.in

@@ -1,4 +1,4 @@
-#! /bin/sh
+#! @IPSEC_SHELL@
 # prefix command to run stuff from our programs directory
 # Copyright (C) 1998-2002  Henry Spencer.
 # Copyright (C) 2006 Andreas Steffen