run by mimetype feature

[edscott wilson garcia]

I can't remember who asked for the feature, but now implemented in CVS
HEAD is the following:

If a valid path (not a directory) is specified as an argument in the
command line of xffm or xftree4, the mimetype associated program will be
used to open the program without loading any xffm libraries or modules
(except the mime module, of course). If no valid associated program
exists for the mimetype, then xfrun4 will pop up so the user can choose
what application to use to open the file (xfrun4 now accepts a valid
path as an argument to use with the program to be run).