Simplify getSQLForSelect
Simplify getSQLForSelect more
Use a strict check against null
Remove some evil spaces
Make the $alias parameter in the `from` method optional
Make code Ocramius certified
Merge pull request #646 from JeroenDeDauw/noalias

Make the $alias parameter in the `from` method optional
Update docs to relfect the changes to QueryBuilder::from made in #646
Merge pull request #647 from JeroenDeDauw/docs

Update docs to relfect the changes to QueryBuilder::from made in #646