With the talk of potentially merging the core-updates branch, I thought
I should get this patch reviewed, since it triggers a full rebuild.

While working with some Imake-based packages recently, I found that
patch-makefile-SHELL did not like when the SHELL definition contained
arguments.  For example, one package would define::

  SHELL = /bin/sh -e

And patch-makefile-SHELL would turn that into::

  SHELL = /gnu/store/.../bin/bash
  -e

which Make would subsequently choke on.

Thoughts?