mutt: add support for ignore-thread patch

Allows application of the ignore-thread patch listed at
<http://wiki.mutt.org/index.cgi?PatchList>. Adds a new command, ignore-thread,
which ignores and unignores message threads. Ignored threads stay collapsed in
the message list.

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

Formula/mutt.rb

@@ -13,7 +13,8 @@ class Mutt < Formula
       ['--enable-debug', "Build with debug option enabled"],
       ['--sidebar-patch', "Apply sidebar (folder list) patch"],
       ['--trash-patch', "Apply trash folder patch"],
-      ['--with-slang', "Build against slang instead of ncurses"]
+      ['--with-slang', "Build against slang instead of ncurses"],
+      ['--ignore-thread-patch', "Apply ignore-thread patch"]
     ]
   end
 
@@ -28,6 +29,10 @@ class Mutt < Formula
       p << 'http://patch-tracker.debian.org/patch/series/dl/mutt/1.5.21-5/features/trash-folder'
     end
 
+    if ARGV.include? '--ignore-thread-patch'
+      p << 'http://ben.at.tanjero.com/patches/ignore-thread-1.5.21.patch'
+    end
+
     return p
   end