Makefile.in: Introduce new `EXTERNALS' variable

	May I suggest the following patch?

# HG changeset patch
# User Ivan Shmakov <ivan <at> theory.asu.ru>
# Date 1208346332 -25200
# Node ID 293c27a240bca3713111b574e4e0ed326367b0eb
# Parent  5b4c24ac29beb70c456ac65a9f06209c49044c34
Introduce new `EXTERNALS' Make variable.
Makefile.in (EXTERNALS): New variable, as a short cut to
`$(POSIX_EXTERNAL) $(SRFI_27_EXTERNAL)'.
(enough): Use `$(EXTERNALS)'.
(install): Likewise.
(clean): Likewise.
(check): Likewise.

diff -r 5b4c24ac29be -r 293c27a240bc Makefile.in
--- a/Makefile.in	Tue Apr 15 22:26:05 2008 +0700
+++ b/Makefile.in	Wed Apr 16 18:45:32 2008 +0700
@@ -140,6 +140,7 @@ LIBSCHEME48 = c/libscheme48.a
 LIBSCHEME48 = c/libscheme48.a
 POSIX_EXTERNAL = c/posix.so
 SRFI_27_EXTERNAL = c/srfi-27.so
+EXTERNALS = $(POSIX_EXTERNAL) $(SRFI_27_EXTERNAL)
 UNIX_OBJS = c/unix/misc.o c/unix/io.o c/unix/fd-io.o c/unix/event.o
 OBJS =	c/scheme48vm-$(BIT_SUFFIX).o \
 	c/extension.o c/free.o c/double_to_string.o c/bignum.o \
@@ -161,7 +162,8 @@ CONFIG_FILES = scheme/interfaces.scm sch

 # The following is the first rule and therefore the "make" command's
 # default target.