{Matches,DoesNotMatch} support the ESCAPE clause with PostgreSQL

to_SQL already has supported the ESCAPE clause in #318.
PostgreSQL can use the ESCAPE clause too.
Merge pull request #344 from kaznum/support_the_escape_clause_of_postgresql

{Matches,DoesNotMatch} support the ESCAPE clause with PostgreSQL
Allow for handling quoted values in ranges

Since Active Record needs to eagerly cast values, we need to check for
quoted infinity in our range handling
Deprecate automatic type casting within Arel

Rails now performs all casting eagerly, before passing the value into
Arel. Once we remove this, the code on both sides will be simplified
greatly. Ideally, we can provide the appropriate public APIs on the
Rails side to ease this transition for library authors who depend on
this behavior.
Allow a type caster to be given to the `Arel::Table` object

This will allow most consuming code to avoid the deprecation introduced
in 008445d6fd5f825d9b445ac75a7be67f0f7ab52c. The only code which will be
affected is code that is building the `Arel::Table` object manually,
rather than calling `arel_table` on an Active Record class. Hopefully
this case will be rare enough that we don't need to introduce any
additional APIs to work around it.
Remove 1.9 from the Travis builds

Arel 7.0 will not support Ruby 1.9
Change the version to 7.0.0.alpha