don't keep the lease_start in the store, always initialize it to the
current time such that a node will respect another master for at least
an entire lease_period when it wakes up.
sync store before closing tlog
ensure tlfs are synced before renaming them to their destination
add failing drop_master_while_maintenance
make sure lease expired event keep forever flowing through the state machine
prevent slave from ignoring duplicate message from master
a bit more info logging
Merge #450 branch 'incubaid-sync-store' into incubaid-1.6

Conflicts:
	src/node/local_store.ml
	src/node/mem_store.ml
Logging more Paxos at info level
Merge branch 'incubaid-1.6' into masterless

Conflicts:
	src/node/mem_store.ml
	src/paxos/slave.ml
	src/system/drop_master.ml
comment from PR
Merge pull request #460 from Incubaid/masterless

Masterless
Enabling non-LWT logging

Code mostly imported from 1.7 branch, specifically rev.
037abb4024f64af8cd86a3d57668283cefd87598, to reach a state similar as to
the one seen in rev. 186bd73659f277947cf2a95fe71bec27e15d27dc.
Logging embedded in statistics
Add `To_string` module

Implement some utilities in order to be able to write cleaner
`to_string` functions, especially of large records. Better than using
gigantic `Printf.sprintf` templates...
Use `To_string` for some `to_string` implementations
Merge mark-christiaens/logging into 1.6 (using imerge)
Fix compilation
fix for multiple masters issue by respecting the paxos logic
Update `META` and `debian/changelog` for 1.6.12