Try to run compat tests with Rake::TestTask

This should make the compat specs run under integrity
installs at Heroku.

Rakefile

@@ -7,6 +7,8 @@ task :spec => :test
 
 # SPECS ===============================================================
 
+task(:test) { puts "==> Running main test suite" }
+
 Rake::TestTask.new(:test) do |t|
   t.test_files = FileList['test/*_test.rb']
   t.ruby_opts = ['-rubygems'] if defined? Gem
@@ -16,18 +18,17 @@ desc "Run < 0.9.x compatibility specs"
 task :compat do
   begin
     require 'mocha'
+    require 'test/spec'
+    at_exit { exit 0 } # disable test-spec at_exit runner
+
+    puts "==> Running compat test suite"
+    Rake::TestTask.new(:compat) do |t|
+      t.test_files = FileList['compat/*_test.rb']
+      t.ruby_opts = ['-rubygems'] if defined? Gem
+    end
   rescue LoadError
-    puts 'WARN: skipping compat tests. mocha gem required.'
-    next
+    warn 'Skipping compat tests. mocha and/or test-spec gems not installed.'
   end
-
-  if ! system('specrb --help &>/dev/null')
-    puts 'WARN: skipping compat tests. test-spec gem required.'
-    next
-  end
-
-  pattern = ENV['TEST'] || '.*'
-  sh "specrb --testcase '#{pattern}' -Ilib:test compat/*_test.rb"
 end
 
 # PACKAGING ============================================================