kernel - Finish implementing PG_RAM / pipelined mmap operation

kernel - Finish implementing PG_RAM / pipelined mmap operation

* Finish implementing the PG_RAM read-ahead mark code.  This code
  allows the VM system to generate pipelining faults when reading a
  memory mapped file sequentially.

  This allows programs which scan files via mmap() to max-out the I/O system,
  similar to read().  Before this change programs using mmap() could not get
  better then ~70-80% disk utilization for sequential I/O.

  This commit passes the sequential access flag through to the VOP_GETPAGES
  code which then adjusts the sequential access heuristic in the ioflags
  accordingly.