speed up startup (avoid loading some gems on startup)

correct group permission leaks
add Discourse.cache for richer caching support

spec/components/cache_spec.rb

@@ -0,0 +1,63 @@
+require 'spec_helper'
+require 'cache'
+
+describe Cache do
+
+  let :cache do
+    Cache.new
+  end
+
+  it "can delete by family" do
+    cache.fetch("key2", family: "my_family") do
+      "test"
+    end
+
+    cache.fetch("key", expires_in: 1.minute, family: "my_family") do
+      "test"
+    end
+
+    cache.delete_by_family("my_family")
+    cache.fetch("key").should be_nil
+    cache.fetch("key2").should be_nil
+
+  end
+
+  it "can delete correctly" do
+    r = cache.fetch("key", expires_in: 1.minute) do
+      "test"
+    end
+
+    cache.delete("key")
+    cache.fetch("key").should be_nil
+  end
+
+  it "can store with expiry correctly" do
+    $redis.expects(:get).with("key").returns nil
+    $redis.expects(:setex).with("key", 60 , "bob")
+
+    r = cache.fetch("key", expires_in: 1.minute) do
+      "bob"
+    end
+    r.should == "bob"
+  end
+
+  it "can store and fetch correctly" do
+    $redis.expects(:get).with("key").returns nil
+    $redis.expects(:set).with("key", "bob")
+
+    r = cache.fetch "key" do
+      "bob"
+    end
+    r.should == "bob"
+  end
+
+  it "can fetch existing correctly" do
+
+    $redis.expects(:get).with("key").returns "bill"
+
+    r = cache.fetch "key" do
+      "bob"
+    end
+    r.should == "bill"
+  end
+end