use Array#uniq in AM instead of deprecated Array#uniq_by

deprecate String#encoding_aware? and remove its usage

auto_explain_threshold_in_seconds should be a global config option so it can be shared between AR::Base and AR::Model

1) Adding gzip to pages cache, closes #4124

2) Allow scaffold/model/migration generators to accept a "index" and "uniq"
modifiers, as in: "tracking_id:integer:uniq" in order to generate (unique)
indexes. Some types also accept custom options, for instance, you can
specify the precision and scale for decimals as "price:decimal{7,2}".
This feature closes #2555.

added ability to specify from cli when generating a model/migration whether particular property should be an index like this 'rails g model person name:string:index profile:string'

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

remove ruby 1.8 stuff method skip to support ruby 1.8 series

remove Rails application fallback from AD::IntegrationTest

remove checking for non-empty string before calling to_sym