sqlite: "optionally" depend on readline

Using readline rather than libedit allows, among other things, the
sharing of the same line-editing config file (.inputrc) across BSDish
and Linux systems. And I'm lazy, and don't want to learn how to
configure editline.

We currently just throw away :optional when processing dependencies, so
if someone really wants libedit instead, we can either make this into an
install option (--with-readline) or vice-versa (--with-libedit).

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

Formula/sqlite.rb

@@ -12,6 +12,8 @@ class Sqlite < Formula
   sha1 'a9da98a4bde4d9dae5c29a969455d11a03600e11'
   version '3.7.9'
 
+  depends_on 'readline' => :optional
+
   def options
   [
     ["--with-rtree", "Enable the R*Tree index module"],