Description of problem:
The "Create archive" context menu in Nautilus does not allow a
single-file bz2 or gz archive to be created. The dialog box (which
should really allow an archive type to be selected, rather than going
by the file extension alone) allows a single file (for example, an ISO
cdrom image) to be compressed to an iso.tar.gz or iso.tar.bz2, but
removing the .tar in order to create a simple iso.bz2 results in the
error "Archive not supported".

Version-Release number of selected component (if applicable):
file-roller-2.8.1-1

How reproducible:
Always

Steps to Reproduce:
1. Right-click on an ISO file, choose "Create archive"
2. Edit the archive name so that it ends in .iso.gz rather than
.iso.tar.gz
3. Press Create 
  
Actual results:
"Archive not supported"

Expected results:
A single-file .iso.gz archive should be created, and some options
should be visible in the dialog to allow archive type to be selected,
rather than having the user edit an extension.