Import Data.ByteString.Lazy, improve ByteString Fusion, and resync with FPS head

Import Data.ByteString.Lazy, improve ByteString Fusion, and resync with FPS head

This patch imports the Data.ByteString.Lazy module, and its helpers,
providing a ByteString implemented as a lazy list of strict cache-sized
chunks. This type allows the usual lazy operations to be written on
bytestrings, including lazy IO, with much improved space and time over
the [Char] equivalents.