adding client_encoding method for discovering the encoding set for this client, testing exec_insert on a string

There're a lot of places in Rails source code which make a lot of sense to switching to Object#in? or Object#either? instead of using [].include?.

Disable IdentityMap in log tests, it's not important and when running tests rake task it logs more messages in the tested buffer.
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

- When a :_destroy truthiness is provided in the attributes hash, the
  record should get destroyed regardless of the result of the proc or
    method supplied to :reject_if. (If :allow_destroy is true)

[#6006 state:committed]
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

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

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

The author of ERB sais, his eRuby implementation was originally named "ERb/ERbLight" and then renamed to "ERB" when started bundled as a Ruby standard lib.
http://www2a.biglobe.ne.jp/~seki/ruby/erb.html