Allow changing existing columns in schema builder
Added the ability to specify the column after which a new column should be added (for MySQL).

Signed-off-by: Maarten Staa <aistina@gmail.com>
Added the ability to add database enum columns, natively for MySQL and Postgres, and emulated via strings in SQLite and SQL Server.

Signed-off-by: Maarten Staa <aistina@gmail.com>
Merge remote-tracking branch 'origin/master'

Conflicts:
	laravel/database/schema/grammars/postgres.php
	laravel/database/schema/grammars/sqlite.php
	laravel/database/schema/grammars/sqlserver.php
	laravel/database/schema/table.php

Signed-off-by: Maarten Staa <aistina@gmail.com>