made gridview plural rule compatible with ICU version < 4.8

issue #1072
added unit test to verify storing of null values

http://www.yiiframework.com/forum/index.php/topic/48359-inserting-nulls/page__view__findpost__p__226019
fixed unit tests for cubrid and postgresql

both do not support unsigned integers
refactored Component::off().
Fixes #1025: Implemented support for class-level events.
Typo [skip ci]
Merge pull request #1101 from lucianobaraglia/master

Typo [skip ci]
Added note about "Inconsistent types declared for an argument: U_ARGUMENT_TYPE_MISMATCH" ICU error to i18n docs