fix for multiple masters issue by respecting the paxos logic
randomize lease expired & election timeout
address comments from PR
at end of collapse, replaced copy with a rename.
don't sync a readonly store
(cherry picked from 459d03d37f8183ba908e20576a1fb8578d0bf872)
addressing comments;
making sure a double close doesn't hurt
Merge pull request #473 from Incubaid/backport

don't sync a readonly store
comments
Merge branch '1.6' into ARAKOON-474

Conflicts:
	src/node/store.ml
Merge pull request #474 from Incubaid/ARAKOON-474

at end of collapse, replaced copy with a rename.
META and changelog for 1.6.13
Merge pull request #470 from Incubaid/multiple-masters

Multiple masters
Merge pull request #475 from Incubaid/prepare-1.6.13

META and changelog for 1.6.13
Merge origin/1.6 into 1.6-for-1.7 (using imerge)
Indentation fixups
Merge pull request #476 from Incubaid/1.6-for-1.7

1.6 for 1.7
Add `Client_main.find_master'`

This patch adds `Client_main.find_master'`, which should be a more
resilient master lookup algorithm.

It also reworks `Client_main.find_master` to use the new `find_master'`,
but keep the behaviour of the original action regarding error handling.
make closing a tlog with the correct marker a bit easier
Implement concurrent connecting
Fix exception handling in `Client_main.with_connection'`