online model copy in classifier
add version.hpp
remove `is_updated_` flag
use byte_buffer instead of std::string for binary data
Add permission check to datadir
Merge pull request #590 from kumagi/feature/online_model_copy

online model copy in classifier
Merge pull request #610 from rimms/check_permission_of_datadir

Add permission check to datadir
Refactor get_ip function
Eliminate unsed include
Remove server::common::util namespace from util.cpp and signals.cpp

fixes #190
`is_writable` should be out of `util`
Merge pull request #589 from jubatus/refactor-util

Refactor server/common/util