gambit-scheme/scheme48 conflict

Formula/gambit-scheme.rb

@@ -5,6 +5,8 @@ class GambitScheme < Formula
   url 'http://www.iro.umontreal.ca/~gambit/download/gambit/v4.7/source/gambc-v4_7_0.tgz'
   sha256 '2b03ecef89da2a53212dc3e6583ee4175d91a0752779e1758bcab5d09e9d1e63'
 
+  conflicts_with 'scheme48', :because => 'both install `scheme-r5rs` binaries'
+
   option 'with-check', 'Execute "make check" before installing'
   option 'enable-shared', 'Build Gambit Scheme runtime as shared library'
 

Formula/scheme48.rb

@@ -5,6 +5,7 @@ class Scheme48 < Formula
   url 'http://s48.org/1.9/scheme48-1.9.tgz'
   sha1 '8fd78d328a8c39ecd848e849ade094c30c2bb4ba'
 
+  conflicts_with 'gambit-scheme', :because => 'both install `scheme-r5rs` binaries'
   conflicts_with 'scsh', :because => 'both install include/scheme48.h'
 
   def install