CCBC-183 Improve lcb_get_replica()

Now it is possible choose between three strategies:

1) LCB_REPLICA_FIRST: previously accessible and default now, when the
   caller will get first successful replica or error

2) LCB_REPLICA_ALL: Ask all replicas to send keys

3) LCB_REPLICA_SELECT: select particular replica by the index (from 1
   to 3 inclusive). This one is faster, but can generate false
   negatives

Change-Id: Ib50a578d6ac99a0e1cb05c6a6a82b7c0c13082a5
Reviewed-on: http://review.couchbase.org/27308
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Fixup typo about replica indexes: they are zero-based

Change-Id: Ibe87f8f03a5e4bd577c1435bb53affcb2789afb5
Reviewed-on: http://review.couchbase.org/27347
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Added a note about replica order, minor phrasing.

Change-Id: I04c092ac88dd3baefdd4bf248b11809a6dd69363
Reviewed-on: http://review.couchbase.org/27350
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Update metadata for release 2.0.7

Change-Id: Iafaf9f72b3ca278a41c3a49394c407ab9b49c1c6
Reviewed-on: http://review.couchbase.org/27349
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Set date in RELEASE_NOTES

Change-Id: I5fce32f97913a3e2e073be4b367eb0d0114ecc2b
Reviewed-on: http://review.couchbase.org/27352
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>