Avoid casting of OIDs to fix compat with Redshift database

[larskanis]

Redshift doesn't support OID these casts, so we do OID lookup through the pg_proc table and add type 'name' as an alias for 'text'.

Also clean up the type map generation, so that only arrays are separated and all other types can be registered.

Fixes #369

[larskanis]

@TSMMark Could you try this PR with Redshift?

[TSMMark]

yes will report back after tested

[TSMMark]

@larskanis Sorry but my bundler isn't allowing me to install the pg gem using this commit hash ref, so I'm not able to dig into it and test right now

gem "pg", git: "https://github.com/larskanis/ruby-pg.git", ref: "365008ef71118da01dc9b3f422c9a81ae62602ad"

Bundler could not find compatible versions for gem "pg":
  In Gemfile:
    postgres_to_redshift was resolved to 0.1.2, which depends on
      pg (~> 1.2.0)

    redshift_simple_migrator was resolved to 0.2.1, which depends on
      pg (>= 0.18)

    sequel-redshift was resolved to 0.0.2, which depends on
      pg

    sequel_pg was resolved to 1.14.0, which depends on
      pg (>= 0.18.0, != 1.2.0)

Could not find gem 'pg (~> 1.2.0)', which is required by gem 'redshift_simple_migrator', in any of the relevant sources:
  https://github.com/larskanis/ruby-pg.git (at 365008e@365008e)

Maybe I'm doing something wrong

[larskanis]

The dependency of postgres_to_redshift gem is too strict. I relaxed it in larskanis/postgres_to_redshift@d107914

So this file resolves for me:

source "https://rubygems.org"

gem "pg", git: "https://github.com/larskanis/ruby-pg.git", ref: "365008ef71118da01dc9b3f422c9a81ae62602ad"
gem "postgres_to_redshift", git: "https://github.com/larskanis/postgres_to_redshift", ref: "d1079144e632fb09f3e4cf5bd095dceffa97360c"
gem "redshift_simple_migrator"
gem "sequel-redshift"
gem "sequel_pg"

[TSMMark]

That indeed resolves. Should be able to test soon

[TSMMark]

LGTM