Support for specifying column in condition.

Nice to have ability to passing on instance of Column as part of condition.
Helpful to build complex query.

Example:
```
where()->equals( new Column("aCol", "tmpTable"), 1);
```

Author: prasad83

src/Syntax/Where.php

@@ -267,7 +267,8 @@ public function compare($column, $value, $operator)
     private function prepareColumn($column)
     {
         //This condition handles the "Select as a a column" special case.
-        if ($column instanceof Select) {
+        //or when compare column is customized.
+        if ($column instanceof Select || $column instanceof Column) {
             return $column;
         }