Added new bochsrc option to control the speaker output mode. The choices 'sound'
(lowlevel sound output), 'system' (system beep on Linux and Windows) and 'gui'
(forward beep to related gui methods) are available.


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@11720 6c8e4198-a580-4521-a02f-c9ae86df1db9