Blahtexml: use options dsl

Formula/blahtexml.rb

@@ -5,17 +5,14 @@ class Blahtexml < Formula
   url 'http://gva.noekeon.org/blahtexml/blahtexml-0.9-src.tar.gz'
   md5 'ed790599223c2f8f6d205be8988882de'
 
-  depends_on 'xerces-c' unless ARGV.include? '--blahtex-only'
-
-  def options
-    [['--blahtex-only', "Build only blahtex, not blahtexml"]]
-  end
+  option 'blahtex-only', "Build only blahtex, not blahtexml"
 
+  depends_on 'xerces-c' unless build.include? '--blahtex-only'
 
   def install
     system "make blahtex-mac"
     bin.install 'blahtex'
-    unless ARGV.include? '--blahtex-only'
+    unless build.include? '--blahtex-only'
       system "make blahtexml-mac"
       bin.install 'blahtexml'
     end