liblo: support --HEAD builds

Closes Homebrew/homebrew#19059.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/liblo.rb

@@ -5,6 +5,14 @@ class Liblo < Formula
   url 'http://downloads.sourceforge.net/project/liblo/liblo/0.26/liblo-0.26.tar.gz'
   sha1 '21942c8f19e9829b5842cb85352f98c49dfbc823'
 
+  head 'git://liblo.git.sourceforge.net/gitroot/liblo/liblo'
+
+  if build.head?
+    depends_on 'autoconf' => :build
+    depends_on 'automake' => :build
+    depends_on 'libtool' => :build
+  end
+
   option "enable-ipv6", "Compile with support for ipv6"
 
   def install
@@ -14,7 +22,12 @@ class Liblo < Formula
 
     args << "--enable-ipv6" if build.include? "enable-ipv6"
 
-    system "./configure", *args
+    if build.head?
+      system "./autogen.sh", *args
+    else
+      system "./configure", *args
+    end
+
     system "make install"
   end
 end