Fix grammatical errors.
update dependency for 0.6.0 deb package
improve log messages
improve exception message
Merge pull request #822 from jubatus/improve-logs

Improve logs and exception messages in server
Merge pull request #817 from jubatus/deb-0.6.0

update dependency for 0.6.0 deb package
update dependency for 0.6.0 rpm package
update README
unregister membership from ZK before stop server
append `close_lock_service()` for `prepare_for_stop()`
revert cht::find lost in #822
Merge branch 'grammatical-error' of github.com:gwtnb/jubatus into gwtnb-grammatical-error

Conflicts:
	jubatus/server/common/config.cpp
eliminate warnings (refs #822)
regenerate proxy code to apply jenerator change made in #822
Fix linear_mixer to output size of put_diff: refs #806
Merge pull request #828 from jubatus/fix-mix

(develop) Fix linear_mixer logging
Merge pull request #813 from jubatus/debug/fix_delete_watcher_behavior

Session with ZooKeeper should closed before server stopped
Remove warnings (Fix #827)
Merge pull request #829 from gwtnb/remove-warnings

Remove warnings (Fix #827)
add requirements for building RPM package in README