Optimized mysql++.h: 	- Only #including query.h and compare.h, as it's the minimum set 	  that brings in everything except custom*.h. 	- Added idempotency guard around header contents, to reduce 	  compile time if this header is included multiple times 	- Updated Doxygen file comment to explain why these two 	  #includes are sufficient, and to better explain why #including 	  mysql++.h is the most reasonable choice for end-user programs.
Optimized mysql++.h:
	- Only #including query.h and compare.h, as it's the minimum set
	  that brings in everything except custom*.h.
	- Added idempotency guard around header contents, to reduce
	  compile time if this header is included multiple times
	- Updated Doxygen file comment to explain why these two
	  #includes are sufficient, and to better explain why #including
	  mysql++.h is the most reasonable choice for end-user programs.


git-svn-id: 1a57124bbb9aca193a920d0ffd753d488afb922b@640 5946f024-35f4-0310-b1b3-9a3be3380cfb

veprbl/mysqlpp,veprbl/mysqlpp,veprbl/mysqlpp