Some fixes / improvements in logging system
- fixed pluginlog init in non-plugin mode
- reduced logprefix length limit and use it for the related string parameter
- increase the device prefix size to 6
- TODO: change some more device prefixes


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12080 6c8e4198-a580-4521-a02f-c9ae86df1db9