Add known values for InitFlags
Saner identifiers for kernel receive buffer size limits
Enforce outgoing InitResponse.MaxWrite values to fit in buffer
Pass kernel receive buffer size as OS X mount option `iosize`
Increase kernel receive buffer size to 128 KiB
Use the 128 KiB kernel receive buffer; set fuse.InitBigWrites

This is not directly tied to the constant because of package
boundaries. This FSIniter API will change to remove this wart.