Fixes #2079

- DbMessageSource now performs UNION ALL.
- Fixed message merging for php and po.
- Updated tests.

Conflicts:
	framework/CHANGELOG.md

Update QueryBuilder.php and Query.php

Added one line about support of UNION ALL queries.

Comment test because it proceed an errors when tries to run at mssql and other DBMS.

Change <code>array_reduce</code> with anonimous function variant to easy string collection from pieces of unions.

Using short array syntax.

issue #1797

Add test for UNION/UNION ALL function.
It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.

Change buildUnion method to be ready to accept parameters in <code>['all' => $all, 'query' => $query]</code> format for division to "UNION" and "UNION ALL" constructions.

Change passing parameters to array with two elements – 'all' which means if we use UNION or UNION ALL construction and 'query' which is our sql query that will be at right of construction.

in case no dir is present

Forget one ";" :D

Delete some spaces from result string.

Change union method to accept also <code>$all</code> variable. TRUE means that we must results <code>UNION ALL</code> construction, FALSE – that <code>UNION</code>.

Fixed some errors – syntax with ";" after closure function and also moved building of unions queries into this function.

Change using of implode to convert array of queries to union to array_reduce. Result of this changing is that code feel difference between two selects that connects with UNION and two selects that connects with UNION ALL.

#2103 improves http exception consistency and adds new subclasses

- i18n now falls back to `en` from `en-US` if message translation isn't found
- View now falls back to `en` from `en-US` if file not found
- Default `sourceLanguage` and `language` are now `en`

Adjustment the translation into Portuguese of Brazil.

Added ability to get incoming headers

Fixes #1958: `beforeSubmit` in `yii.activeform` is now executed after validation and before form submission