Render ExcludeContraint Column as column, not plain string

Render ExcludeContraint Column as column, not plain string

Fixed bug where autogenerate of :class:`.ExcludeConstraint`
would render a raw quoted name for a Column that has case-sensitive
characters, which when invoked as an inline member of the Table
would produce a stack trace that the quoted name is not found.
An incoming Column object is now rendered as ``sa.column('name')``.

Change-Id: Ic84fc0b0fbaa5816ece1944043cd01a653bfe4ce
Fixes: #478