Proper single character switch handling

Includes a test. So now you can do `brew cleanup -ns` and it will work.

Library/Homebrew/extend/ARGV.rb

@@ -103,6 +103,16 @@ module HomebrewArgvExtension
     return false
   end
 
+  # eg. `foo -ns -i --bar` has three switches, n, s and i
+  def switch? switch_character
+    return false if switch_character.length > 1
+    options_only.each do |arg|
+      next if arg[1..1] == '-'
+      return true if arg.include? switch_character
+    end
+    return false
+  end
+
   def usage
     require 'cmd/help'
     Homebrew.help_s

Library/Homebrew/test/test_ARGV.rb

@@ -30,4 +30,19 @@ class ARGVTests < Test::Unit::TestCase
     assert_raises(FormulaUnavailableError) { ARGV.formulae }
   end
 
+  def test_switch?
+    ARGV.reset
+    ARGV.unshift "-ns"
+    ARGV.unshift "-i"
+    ARGV.unshift "--bar"
+    assert ARGV.switch?('n')
+    assert ARGV.switch?('s')
+    assert ARGV.switch?('i')
+    assert !ARGV.switch?('b')
+    assert !ARGV.switch?('ns')
+    assert !ARGV.switch?('bar')
+    assert !ARGV.switch?('--bar')
+    assert !ARGV.switch?('-n')
+  end
+
 end