Cleaned up superfluous method definitions for Rails 4
* Made :name and :indexes accessors in ::TableDefinition Rails 3
  specific.  Both are covered by readers in Rails 4 and the latter
  also has a writer.
* Modified ::SchemaStatements#create_table_with_schema_plus to only
  attempt to set the table_definition.name for Rails 3 - Rails 4
  already does this in the initialization of the table definition.
  This is the only place I could identify in the schema_plus codebase
  that attempts to set name, and since the value is what Rails 4 does
  by default the code is unnecessary and removes any need for the
  :name attribute writer.
* Eliminated redundant initialization of @indexes in
  ::TableDefinition#initialize_with_schema_plus for Rails 4 (this
  is handled by the Rails 4 initializer).
* Eliminated ::TableDefinition#index for Rails 4 - this was simply
  a copy of the code in Rails 4, and in any event it was being
  shadowed because #index is defined on the real TableDefinition in
  Rails 4 and thus the one defined in schema_plus never got called!