tune ByteStringInputStream for composites

[brharrington]

Adjusts the ByteStringInputStream to work better for composite
ByteString objects. Before it was using asByteBuffer which
forces a compaction on composite types. Now it uses the
asByteBuffers method. This results in a large reduction in
allocations and increase in throughput.

Throughput

Benchmark	Before	After	% Delta
compositeInputStream	31.8	137.6	332.9
compositeToArray	44.6	46.2	3.5
inputStream	115.1	126.5	9.9
toArray	42.8	45.0	5.2

Allocations

Benchmark	Before	After	% Delta
compositeInputStream	104,887,113.5	69,769.8	-99.9
compositeToArray	104,875,451.8	104,875,038.6	-0.0
inputStream	8,418.3	7,987.6	-5.1
toArray	104,874,398.1	104,874,682.8	0.0