Add support for streaming pack / unpack to the API.

--HG--
rename : src/packing/packing_api.c => src/packing/pack_api.c
rename : src/packing/packing.c => src/packing/pack_impl.c
rename : src/packing/packing.c => src/packing/pack_stream.c
Move edits from (local) wiredtiger.h to wiredtiger.in.
Edit wiredtiger.in, not wiredtiger.h.
Add documentation and checking to pack streams, return the number of bytes (un)packed.
Fix pack_close: read fields before freeing the struct.
Add a schema generation number to avoid using stale table structures.

This is a stop-gap at best, until tables use the same caching and locking as btree handles.
typo
Add new exported symbols
Style cleanups: long lines, new spelling.
Commit a test to ensure session table cache is invalidated.
Make run-time statistics optional, defaulted to "off".

Change statistics_log to pay attention to the new statistics flag
(this means you can turn statistics logging on/off by reconfiguring
the statistics flag).

Don't allocation statistics structures separately from the enclosing
objects, it simplifies error handling a lot.

Fix a bug in re-configuration, we should only review the application-
specified values, and verbose configuration wasn't doing that.
Merge branch 'develop' into statistics

Conflicts:
	src/config/config_def.c
	test/format/wts.c
Run more of the wiredtiger_open calls by closing previously opened handles.
Change it so that statistics_log configures statistics as well.
Merge pull request #463 from wiredtiger/statistics

Make run-time statistics optional.
Merge pull request #461 from wiredtiger/pack-streams

Add support for streaming pack / unpack to the API.
Don't export packing streams to Java or Python: they have their own solutions.
Fix complaints from s_style.
include/packing.i:315:3: error: 'pv.type' may be used uninitialized in this function
Always set pv->havesize to indicate whether there is a size in the packing string.
Conditional jump or move depends on uninitialised value(s)
==72089==    at 0xDCFD43E: __pack_size (packing.i:184)