Bumped minimum Boost version required to v1.55.

Now uses Boost v1.55's new much more efficient get_exception_ptr() method on futures.

Added don't initialise flag to Aligned_Allocator.hpp

Fixed small bug where exception_ptr * was null where it shouldn't have been for immediate completions.

Find in files AFIO is now able to hit 2Gb/sec.
Removed the unnecessary shared_ptr to the dispatcher being held by every file handle now that dispatchers won't destruct until all ops have finished.
Added memory mapped file support.

Fixed uninit data in aligned_allocator with initialisation off.

Finished find in files AFIO.