fix typo
fix link in documentation
Merge pull request #431 from deeky666/DBAL-683

[DBAL-683] Fix link to known vendor issues in documentation
set mysqli driver options before real connect
Merge pull request #432 from deeky666/fix-mysqli-driver-options

Fix mysqli driver options
fix adding primary key during table alteration in MySQL
Merge pull request #435 from deeky666/DBAL-400

[DBAL-400] Fix adding primary key during table alteration in MySQL
Added column collation support for MySQL, SQLite and PostgreSQL
Fixed calculation of differences of columns
A column comment can be only string