Add support for different AXL transfer types

[tonyhutter]

FILO should be modified to allow the user to pick a AXL transfer type. Currently, it just uses SYNC.

[adammoody]

We'll need to be able to specify the AXL transfer type on a per transfer basis, perhaps an argument to Filo_Flush. A single run can have output sets in multiple places, like both the ramdisk and the IBM BB. For those, we want to pick different transfer types depending on the source and destination, like pthread for ramdisk and bbapi for the BB.