rafthttp: fix import
Merge pull request #1762 from xiang90/fix_import

rafthttp: fix import
Merge pull request #1761 from xiang90/fix_raft

raft: should not decrease match and next when handling out of order msgAppResp
raft: raft.restore should never truncate the log at current term.

A raft state machine might receive out of date snapshot due to network latency.
A raft state machine MUST NOT truncate its matched log entries of current term
when it tries to restore a snapshot.