Dump backtrace to rack.errors on unhandled exception

Also added a dump_errors option so that this can be disabled
when necessary.

CHANGES

@@ -1,5 +1,9 @@
 = 0.9.0 (unreleased)
 
+ * New "dump_errors" option controls whether the backtrace is dumped to
+   rack.errors when an exception is raised from a route. The option is
+   enabled by default for top-level apps.
+
  * New ":provides" route condition takes an array of mime types and
    matches only when an Accept request header is present with a
    corresponding type. [cypher]

lib/sinatra/base.rb

@@ -411,6 +411,12 @@ module Sinatra
       invoke handler unless handler.nil?
     rescue ::Exception => boom
       @env['sinatra.error'] = boom
+
+      if options.dump_errors?
+        msg = ["#{boom.class} - #{boom.message}:", *boom.backtrace].join("\n ")
+        @env['rack.errors'] << msg
+      end
+
       raise boom if options.raise_errors?
       @response.status = 500
       invoke errmap[boom.class] || errmap[Exception]
@@ -660,6 +666,7 @@ module Sinatra
     end
 
     set :raise_errors, true
+    set :dump_errors, false
     set :sessions, false
     set :logging, false
     set :methodoverride, false
@@ -753,6 +760,7 @@ module Sinatra
 
   class Default < Base
     set :raise_errors, false
+    set :dump_errors, true
     set :sessions, false
     set :logging, true
     set :methodoverride, true

test/mapped_error_test.rb

@@ -50,6 +50,18 @@ describe 'Exception Mappings' do
     body.should.equal 'looks good'
   end
 
+  it 'dumps errors to rack.errors when dump_errors is enabled' do
+    mock_app {
+      set :raise_errors, false
+      set :dump_errors, true
+      get('/') { raise FooError, 'BOOM!' }
+    }
+
+    get '/'
+    status.should.equal 500
+    @response.errors.should.match(/FooError - BOOM!:/)
+  end
+
   it "raises without calling the handler when the raise_errors options is set" do
     mock_app {
       set :raise_errors, true