ngspice: build with xspice support

xspice provides compatibility with keyfeatures from spice2 which are
absent from spice3. This means many models available on the internet or
from manufactures which were written in spice2 will be compatible with
ngspice.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/ngspice.rb

@@ -1,19 +1,27 @@
 require 'formula'
 
 class Ngspice < Formula
-  url 'http://downloads.sourceforge.net/project/ngspice/ng-spice-rework/24/ngspice-24.tar.gz'
   homepage 'http://ngspice.sourceforge.net/'
+  url 'http://downloads.sourceforge.net/project/ngspice/ng-spice-rework/24/ngspice-24.tar.gz'
   md5 'e9ed7092da3e3005aebd892996b2bd5f'
 
+  def options
+    [["--without-xspice", "Build without x-spice extensions"]]
+  end
+
   def install
-    system "./configure", "--disable-debug", "--disable-dependency-tracking",
-                          "--prefix=#{prefix}",
-                          "--with-editline=yes",
-                          "--enable-x"
+    args = ["--disable-debug",
+            "--disable-dependency-tracking",
+            "--prefix=#{prefix}",
+            "--with-editline=yes",
+            "--enable-x"]
+    args << "--enable-xspice" unless ARGV.include? "--without-xspice"
+
+    system "./configure", *args
     system "make install"
   end
 
-  def caveats
+  def caveats;
     "Note: ngspice is an X11 application."
-  end
+ end
 end