Add support for --enable-builtins to configure

--enable-builtins will allow users to include some extensions in the
WiredTiger library by default. This saves needing to load libraries
at runtime.
More implementation of --with-builtins=

Not yet linking in the library properly.
Link builtin extensions directly into libwiredtiger.la.
Fix zlib builtin build, simplify parsing the list of builtins, don't list "./Makefile" as a generated file.
More --with-builtins implementation.

Backout change to how builtins list is parsed, I was seeing:
../configure: line 5439: printf %s\n: command not found
Fix quoting in m4 script.
Update the API exposed by extensions that can be builtin.

Otherwise multiple builtin extensions will conflict on
the wiredtiger_extension_init function.
Add statistics to track memory from splits that cannot be freed immediately.

refs #1079
Free memory more aggressively after splits.  Keep the list of allocated objects in order, stop scanning when the first object is found that cannot be freed.  Check if there is no other thread active in the tree, and free memory immediately in that case.

refs #1079
If a thread does eviction during a search, it might be holding a reference, so we can't free immediately.

refs #1079
Merge branch 'develop' into builtin-extensions
Merge branch 'develop' into split-memory-management
Merge branch 'develop' into split-memory-management
Add all possible statistics operations (DECRV and ATOMIC flavors)
If all objects stashed by a split are freed, reset the count to zero.
Use a split generation number to determine when memory replaced by a split can be freed.
Take WT_ALLOC_OVERHEAD into account when calculating memory moved between pages by splits.  Always to an increment and a decrement to the page to balance out the overhead added there.
Get rid of the WT_REF.key.pkey field, it's simpler and more explicit to
cast the key.ikey field to a (uintptr_t).
Merge branch 'develop' into onpage-cell
Convert row-store fast on-page key processing from per-page to per key.
Reference #1030, #1038.