Detect IO errors in save
Remove unnecessary logs
Devide open error and read/write error
Detect IO error in load
Remove incomplete file
mix number should be output as ordinal number fix #552
don't mix when no update observed, fix #181
Add warning message when failed to remove
works good in case that version is more than 100th
Fixed wrong message
Merge pull request #698 from rimms/fearute/detect_ioerrors

Detect IO errors in save
Add stdio.h include for remove (3) function: refs #698
cpplint ok
avoid infinite loop in `get_model` fix #711
add test
add do_mix rpc
Merge pull request #708 from jubatus/feature/dont_mix_without_update

don't mix when no update observed, fix #181
Merge pull request #705 from jubatus/feature/ordinal_mix_counting

ordinal mix counting
avoid unneeded double check
exclude `update_members()` because retrying node choice is invoked by selecting oneself