Only allow --interactive with one formula argument

See comments in commit for details.

Library/Homebrew/ARGV+yeast.rb

@@ -66,6 +66,9 @@ module HomebrewArgvExtension
   def quieter?
     flag? '--quieter'
   end
+  def interactive?
+    flag? '--interactive'
+  end
 
   def flag? flag
     options.each do |arg|

Library/Homebrew/brew.h.rb

@@ -174,7 +174,7 @@ end
 
 def install f
   f.brew do
-    if ARGV.flag? '--interactive'
+    if ARGV.interactive?
       ohai "Entering interactive mode"
       puts "Type `exit' to return and finalize the installation"
       puts "Install to this prefix: #{f.prefix}"

bin/brew

@@ -90,6 +90,15 @@ begin
           puts "#{f}: #{ENV[f]}" unless ENV[f].to_s.empty?
         end
       end
+      
+      if ARGV.interactive? and ARGV.formulae.count > 1
+        # the reason for this is interactive mode is a little tricky to do 
+        # with more than one formula, AND I can't think of a time where you'd
+        # want to do it anyway. If someone comes up with a legitimate use for
+        # this we will adapt the code. "But I might want it!" is not a
+        # legitimate use!
+        raise "Interactive mode can only be used with one formula argument"
+      end
 
       unless ARGV.force?
         unless system "which #{ENV['CC'] or 'cc'} &> /dev/null" and $?.success?