.Count() should always use ToSnake'd foreign keys.

It looks like gorm always uses the snake form of a column by
convention, as seen by searching DBName in scope.go. These counts
were erroring out without the ToSnake'd foreign keys.

Further, the code for has_many and has_one becomes the same (which
makes sense), so I combined the two cases.
Merge pull request #300 from jnfeinstein/master

.Count() should always use ToSnake'd foreign keys.