leaf nodes are different for the same files when using balanced and trickle DAG builders

#### Version information:
go-ipfs version: 0.4.4-
Repo version: 4
System version: amd64/darwin
Golang version: go1.7

#### Type:
Bug

#### Priority:
P1

#### Description:

When encoding the same file using the balanced and the trickle DAG builders separately, both trees end up not sharing any leaf hash.

@whyrusleeping did a preliminary analysis and it's probably due to the fact that the balanced builder uses UnixFS nodes of type `file` and the trickle builder apparently uses the type `raw`, hence the discrepancy.