imported patch multiple-eviction-threads
Only try to allocate memory for eviction workers if they are configured.
Merge branch 'develop' into multiple-eviction-threads
Merge branch 'develop' into multiple-eviction-threads
Merge branch 'develop' into multiple-eviction-threads

Conflicts:
	src/btree/bt_evict.c
Merge branch 'develop' into multiple-eviction-threads
Don't cache the TXN_OLDEST flag: we don't check repeatedly.
Move the checkpoint generation into the btree structure, increment it after turning on the checkpointing flag.
Disable eviction of dirty pages during checkpoints.  There are cases where dirty pages are being written after the checkpoint has gone past, leading to invalid checkpoints on disk.

refs #976
Take the cache size into account when calculating the maximum size of a page in-memory.  Use that calculation in the decision to deepen internal pages.

refs #486
Disable prefix compression by default.
Merge branch 'develop' into multiple-eviction-threads
Fix a bug in LSM where an autocommit transaction wasn't started.

Due to the change to delay allocating transaction IDs for read only
transactions.
Custodial pointer 'user_cconfig' (line 1552) has not been freed or returned
Custodial pointer 'user_tconfig' (line 1552) has not been freed or returned
Minor shuffling of prefix-compression docs (now that prefix-compression
is off by default, the example should be turning it on, not off).
Optionally skip block cleanup and leak memory on connection close.
Reference #845.
Merge pull request #982 from wiredtiger/leak-memory-on-close

Optionally skip block cleanup and leak memory on connection close.
Use the value of the "leak_memory" config item, not its length, to determine whether it is set.

refs #845, #982
Don't run the leak-memory code, it upsets valgrind.
Merge pull request #981 from wiredtiger/prefix-compression-default

Disable prefix compression by default.