Remove deps from Sphinx.

Sphinx can use MySQL or PostgreSQL, and can use the mysql-connector libraries
instead of a full on MySQL install.

Since we don't know what datasource is intended, replace the hard dependency
with explanations in the caveats.

Formula/sphinx.rb

@@ -1,12 +1,9 @@
 require 'formula'
 
 class Sphinx <Formula
-  version '0.9.9'
-  @url='http://www.sphinxsearch.com/downloads/sphinx-0.9.9.tar.gz'
-  @homepage='http://www.sphinxsearch.com'
-  @md5='7b9b618cb9b378f949bb1b91ddcc4f54'
-
-  depends_on 'mysql'
+  url 'http://www.sphinxsearch.com/downloads/sphinx-0.9.9.tar.gz'
+  homepage 'http://www.sphinxsearch.com'
+  md5 '7b9b618cb9b378f949bb1b91ddcc4f54'
 
   def install
     # fails with llvm-gcc:
@@ -16,4 +13,23 @@ class Sphinx <Formula
     system "./configure", "--prefix=#{prefix}", "--disable-debug", "--disable-dependency-tracking"
     system "make install"
   end
+
+  def caveats
+    <<-EOS.undent
+    Sphinx depends on either MySQL or PostreSQL as a datasource.
+
+    You can install these with Homebrew with:
+      brew install mysql
+        For MySQL server.
+
+      brew install mysql-connector-c
+        For MySQL client libraries only.
+
+      brew install postgresql
+        For PostgreSQL server.
+
+    We don't install these for you when you install this formula, as
+    we don't know which datasource you intend to use.
+    EOS
+  end
 end