Dasher depends on glib, and newish glib comes with gio, so use gio's gvfs

Dasher depends on glib, and newish glib comes with gio, so use gio's gvfs
rather than gnome-vfs. There are some niggles left here: file size is given
by the machine independent (MI) off_t=guint64, but read/operations are in
MD size_t, e.g uint32_t, gsize, but some functions use -1 to mean read
until terminating NUL, so we rediscover the standard ctype.h problem, and
loose range because the size now has to be signed -> gssize. The other
niggle is e.g., m=fwrite(,n,,) : we don't handle m<n.

svn path=/trunk/; revision=3605