Add generic wrapper class to common.

This commit adds a class called Generic_Wrapper to Common.

The purpose of this class is really to prevent rewriting the same code
for library IDs every five minutes.....
Make Thread_Utils::Thread use Generic_Wrapper.

This commit makes the Thread_Utils::Thread class use the new
Generic_Wrapper class.

(It also updates Thread_Utils::Thread_pthread for this change.)
Make remaining Thread_Utils::*_pthread use Generic

This commit makes Thread_Utils::Mutex_pthread and
Thread_Utils::Condition_pthread use the Generic_Wrapper class.