prepare for using sound files from out of the source tree

build_tools/sounds.xml

sounds/agent-alreadyon.gsm

sounds/agent-incorrect.gsm

sounds/agent-loggedoff.gsm

sounds/agent-loginok.gsm

sounds/agent-newlocation.gsm

sounds/agent-pass.gsm

sounds/agent-user.gsm

sounds/auth-incorrect.gsm

sounds/auth-thankyou.gsm

sounds/beep.gsm

sounds/beeperr.gsm

sounds/conf-adminmenu.gsm

sounds/conf-enteringno.gsm

sounds/conf-errormenu.gsm

sounds/conf-getchannel.gsm

sounds/conf-getconfno.gsm

sounds/conf-getpin.gsm

sounds/conf-hasjoin.gsm

sounds/conf-hasleft.gsm