Call minstall with $(SHELL) so the user controls the interpreter

Running minstall directly means that /bin/sh is always used as hte
interpreter. If the user needs or wants to use a different shell fo
minstall, they can use the SHELL make variable.

configs/autoconf.in

@@ -31,7 +31,6 @@ SHELL = @SHELL@
 MKLIB_OPTIONS = @MKLIB_OPTIONS@
 MKDEP = @MKDEP@
 MKDEP_OPTIONS = @MKDEP_OPTIONS@
-INSTALL = $(TOP)/bin/minstall
 
 # Python and flags (generally only needed by the developers)
 PYTHON2 = python

configs/default

@@ -30,7 +30,7 @@ MKLIB_OPTIONS =
 MKDEP = makedepend
 MKDEP_OPTIONS = -fdepend
 MAKE = make
-INSTALL = $(TOP)/bin/minstall
+INSTALL = $(SHELL) $(TOP)/bin/minstall
 
 # Tools for regenerating glapi (generally only needed by the developers)
 PYTHON2 = python