Implements transport-specific calls to request and return message buffers.
Renews pool buffer identifiers when recycling. Buffers. This prevents the GC from accidentally re-returning explicitly-returned buffers.
Aligns buffers to the page size for performance over InfiniBand.
Fixes error message and comments FFI of pagesize.
Merge pull request #13 from ps-labs/explicit-calls

Implements transport-specific calls to request and return message buffers.