load and prefer psych as the YAML parser when it is available

activerecord/lib/active_record/base.rb

@@ -1,3 +1,8 @@
+begin
+  require 'psych'
+rescue LoadError
+end
+
 require 'yaml'
 require 'set'
 require 'active_support/benchmarkable'

activerecord/lib/active_record/fixtures.rb

@@ -1,4 +1,10 @@
 require 'erb'
+
+begin
+  require 'psych'
+rescue LoadError
+end
+
 require 'yaml'
 require 'csv'
 require 'zlib'

railties/lib/rails/commands/dbconsole.rb

@@ -1,4 +1,10 @@
 require 'erb'
+
+begin
+  require 'psych'
+rescue LoadError
+end
+
 require 'yaml'
 require 'optparse'
 require 'rbconfig'