[Update] an update to 2431+ will not disable DGIndexNV, NeroAACenc, QAAC or x265 if already enabled


git-svn-id: http://svn.code.sf.net/p/megui/code@2434 a21b8521-4df1-4ed3-b48c-cff5bc73dcb3
[Update] optional packages will only be downloaded/enabled if needed (part II)
         now all external programs are disabled by default


git-svn-id: http://svn.code.sf.net/p/megui/code@2435 a21b8521-4df1-4ed3-b48c-cff5bc73dcb3