add the casting node to the AST at build time

If we add the casting node to the ast at build time, then we can avoid
doing the lookup at visit time.
build quoted strings
build quoted nodes in factory methods
Removed all the fiels in lib/arel/visitors/ which needs dependency on 'a' also fixed the test case for : test/visitors/test_to_sql.rb:22 which pass in the parameter attribute e.g the parameter a.
removed the attribute that was left in for testing
take in to account quoted and translated values
remove the default parameter and updated comment
Merge branch 'rm_a' into ww2lin-rm_a

* rm_a:
  take in to account quoted and translated values