[wip] better reverse engineers the mapping metadata from a database

[bronze1man]

The problem:

1.use symfony2 doctrine:mapping:import from msyql database to annotation
2.use symfony2 doctrine:schema:update will see a lot of sql update about just import database schema.
3.this PR fix eliminate some of those sql update...

has fixed problem:

• column default
• column unsigned (add test)
• column comment
• column type decimal with precision and scale
• table with simple index
• table with unique index

[bronze1man]

please close PR659

[guilhermeblanco]

Implemented a better and more extensible approach here:
3d86c82

[bronze1man]

Thanks