Account for changes in boost dependencies
Account for changes in boost dependencies

Since <boost/thread/thread.hpp> includes some headers which will already
call a boost_system function, recent versions of boost require
-lboost_system before -lboost_thread will work, resulting in a failure
of this test if not accounted for.

Make it try without -lboost_system first, but try again with it added to
$LIBS if that fails.

LeForgeron/povray,eblanca/povray,LogicalKnight/povray,davidgiven/povray,wfpokorny/povray,POV-Ray/povray,UberPOV/UberPOV,FLOWERCLOUD/povray,c-lipka/povray,LeForgeron/povray,FLOWERCLOUD/povray,LogicalKnight/povray,POV-Ray/povray,FLOWERCLOUD/povray,POV-Ray/povray,BentSm/povray,POV-Ray/povray,davidgiven/povray,wfpokorny/povray,c-lipka/povray,UberPOV/UberPOV,LogicalKnight/povray,UberPOV/UberPOV,wfpokorny/povray,wfpokorny/povray,FLOWERCLOUD/povray,LeForgeron/povray,LeForgeron/povray,UberPOV/UberPOV,LeForgeron/povray,LeForgeron/povray,BentSm/povray,LeForgeron/povray,eblanca/povray,BentSm/povray,wfpokorny/povray,FLOWERCLOUD/povray,eblanca/povray,LeForgeron/povray,BentSm/povray,UberPOV/UberPOV,eblanca/povray,c-lipka/povray,FLOWERCLOUD/povray,UberPOV/UberPOV,davidgiven/povray,FLOWERCLOUD/povray,LogicalKnight/povray,davidgiven/povray,davidgiven/povray,LogicalKnight/povray,UberPOV/UberPOV,davidgiven/povray,davidgiven/povray,LogicalKnight/povray,davidgiven/povray,wfpokorny/povray,POV-Ray/povray,LogicalKnight/povray,POV-Ray/povray,c-lipka/povray,LogicalKnight/povray,davidgiven/povray,POV-Ray/povray,wfpokorny/povray,FLOWERCLOUD/povray,LogicalKnight/povray,FLOWERCLOUD/povray