Bump version
Merge pull request #2374 from ogail/version

Bump version
update changelog
Merge pull request #2389 from guangyang/release-0.7.4

update changelog
Merge pull request #2393 from WindowsAzure/release-0.7.4

Release 0.7.4
Merge pull request #2394 from WindowsAzure/master

master to dev for 0.7.4