Match Exceptions to the rows they came from

When importing it may be nice to be able to tell the user that a particular row is where the exception occurred. This allows us to use the loop index to map an exception to a particular row so that programs could provide additional information to the users if desired.
Simplify getNewInstance

getNewInstance doesn't use the $item array, and the writer already has access to the entity metadata so might as well access it internally instead of passing it as an argument.
Pass the entityName to the entityManager clear()

There's no reason to clear the entitymanager of *all* entities. In our case we have pulled some linked associations for a particular workflow, however once the batchSize is up, suddenly doctrine detects new unmanaged entities and suggests adding a cascade={"persist"}. This will cause duplicate records to be created. We tried listening to the onClear event to reload however that presented other issues.

Since the import process shouldn't really affect other things the user may have done this change fixes that by only clearing entities of this particular class type.
Merge pull request #113 from gnat42/patch-4

Pass the entityName to the entityManager clear()
Merge pull request #112 from gnat42/patch-3

Simplify getNewInstance
Merge pull request #110 from gnat42/patch-1

Match Exceptions to the rows they came from