Release 2.4

This release contains a variety of fixes from 2.3-1. For information about new features in major release 2, see Release 2.1.

A dump/restore is not required for those running 2.X.

• Fixed a concurrency issue between the threaded backends and signal handler thread on windows.
• Fixed a issue that parallel query blocked occasionally on windows.
• Fixed the issue that minor version upgrade occurred error on windows, although it is just a result of wrong status checking.
• Fixed some issues related to software package building on CentOS/Debian Linux.