…ain reference to parent Buffer
This is stacked on top of the patch for ARROW-294, will rebase.
Author: Wes McKinney <email@example.com>
Closes #266 from wesm/ARROW-387 and squashes the following commits:
061ef8b [Wes McKinney] Verify BufferReader passes on ownership of parent buffer to zero-copy slices
42a83a4 [Wes McKinney] Remove duplicated includes
3928ab0 [Wes McKinney] Base MemoryMappedFile implementation on common OSFile interface. Add test case for ARROW-340.