libnfc: add option for PN532 UART support

This option is needed for users of libnfc when using devices connected over
serial with an NXP PN532 chipset - like the microBuilder breakout board:
http://www.microbuilder.eu/Projects/PN532.aspx

Signed-off-by: Misty De Meo <mistydemeo@gmail.com>

Formula/libnfc.rb

@@ -7,9 +7,25 @@ class Libnfc < Formula
 
   depends_on 'libusb-compat'
 
+  def options
+    [
+      ['--with-pn532_uart', 'Enable PN532 UART support'],
+    ]
+  end
+
   def install
-    system "./configure", "--disable-debug", "--disable-dependency-tracking",
-                          "--prefix=#{prefix}"
+    args = [
+      "--prefix=#{prefix}",
+      "--disable-debug",
+      "--disable-dependency-tracking" ]
+
+    if ARGV.include? '--with-pn532_uart'
+      args << "--enable-serial-autoprobe"
+      args << "--with-drivers=pn532_uart"
+    end
+
+    system "./configure", *args
+
     system "make install"
   end
 end