wal: save latest state into new WAL

So we could always read out state when open at valid index.
*: add pauseMember test
integration: fix possible early fire in TestWatch
Merge pull request #1860 from yichengq/249

integration: fix possible early fire in TestWatch
*: typofixes

https://github.com/vlajos/misspell_fixer
Merge pull request #1858 from vlajos/typofixes-vlajos-20141204

typofixes - https://github.com/vlajos/misspell_fixer
Merge pull request #1859 from xiang90/pause_test

*: add pauseMember test
etcdserver: close storage when stop
Merge pull request #1839 from yichengq/245

wal: save latest state into new WAL
Merge pull request #1841 from yichengq/246

etcdserver: close storage when stop
integration: improve member tests