Set ACLOCAL_PATH so that things work

This should mean all those formula that pass options to aclocal don't need to anymore, but I'm not risking changing them.

Library/Homebrew/build.rb

@@ -49,7 +49,12 @@ def install f
       ENV.prepend 'LDFLAGS', "-L#{dep.lib}"
       ENV.prepend 'CPPFLAGS', "-I#{dep.include}"
       ENV.prepend 'PATH', "#{dep.bin}", ':'
-      ENV.prepend 'PKG_CONFIG_PATH', dep.lib+'pkgconfig', ':'
+
+      pcdir = dep.lib/'pkgconfig'
+      ENV.prepend 'PKG_CONFIG_PATH', pcdir, ':' if pcdir.directory?
+
+      acdir = dep.share/'aclocal'
+      ENV.prepend 'ACLOCAL_PATH', acdir, ':' if acdir.directory?
     end
   end
 

Library/Homebrew/extend/ENV.rb

@@ -9,6 +9,9 @@ module HomebrewEnvExtension
     delete('CLICOLOR_FORCE') # autotools doesn't like this
     remove_cc_etc
 
+    # make any aclocal stuff installed in Homebrew available
+    ENV['ACLOCAL_PATH'] = "#{HOMEBREW_PREFIX}/share/aclocal" if MacOS.xcode_version < "4.3"
+
     self['MAKEFLAGS'] = "-j#{self.make_jobs}"
 
     unless HOMEBREW_PREFIX.to_s == '/usr/local'