Remove deprecation warning from attribute_missing 

for attributes that are columns.
Merge pull request #11282 from arunagw/deprecation-removed-attribute-missing-activerecord

Remove deprecated `attribute_missing`.
Do not re-save destroyed association on saving parent object

Closes #11450
Merge pull request #11451 from jetthoughts/11450_do_not_resave_destroyed_association

Do not re-save destroyed association on saving parent object
use arel rather than slapping together SQL strings
reorder bind parameters when merging relations
removing useless assingment
save another array allocation
Lock mysql2 version to 0.3.11 since 0.3.12 is failing right now. Check #11457 for details
Added generated unit test for generator generator and new test:generators rake task included in test:all rake task.
Merge pull request #11419 from simi/generator_generator_test

Added generated unit test for generator generator.
`change_column` for PG adapter respects `:array` option.