Merge branch 'release/0.6.4' into develop
Merge branch 'master' into develop
Merge branch 'master' into develop
Remove use of nullptr in test.
Add a macro _GLIBCXX_DEBUG on debug mode to enable libstdc++ debug mode.
Merge pull request #889 from gwtnb/libstdc++-debug

Add a macro _GLIBCXX_DEBUG on debug mode to enable libstdc++ debug mode.
Merge pull request #888 from gwtnb/remove-nullptr-in-test

Remove use of nullptr in test.
remove unused --disable-eigen configure option (fix #890)
Merge pull request #893 from jubatus/fix-890

remove unused --disable-eigen configure option (fix #890)
fix thread ID to be displayed on OS X (fix #874)
avoid define
Merge pull request #894 from jubatus/fix-874

fix thread ID to be displayed on OS X (fix #874)