Improved directory_entry docs.

Fixed bug in directory_entry where int_fetch() wasn't updating internal fetched metadata correctly.

Renamed directory_entry full_lstat() to fetch_lstat() for consistency.

Fixed bug in close() where it was closing fast enumeration directory handles.
Merge remote-tracking branch 'remotes/origin/master' into more_docs_improvements
Added two new examples in readiness for part 2 of the quick start. The AFIO based version is completed untested and almost certainly does not work.
Added op_from_running_id() method to async_file_io_dispatcher_base.
Fixed some excessively anti-old compiler #ifdef's in the examples.
Fixed breakage with forthcoming Boost v1.55. BE WARNED this breaks compat with v1.54, something we'll need to do anyway soon to gain Vicente's new future->get_exception() support.