"Select format by extension" option in Jalview's "Save As" dialog's file type dropdown menu

Selecting a format by typed in extension is a great timesaver and much loved feature of other software (e.g. Gimp).
In a "Save As" file chooser dialog, with this feature "selected" (what "selected" means is to be decided) the user can type in a filename with the extension of the format that they want (e.g. typing "file.stk" would save the file in Stockholm format, "file.blc" in Block format).
The user needs to be able to control whether this is on or off (e.g. by a checkbox, or a special first option in the file format dropdown).

Up for discussion: whether as the user types an extension, the file format dropdown changes to the relevant format. The upside of this is that the user can see the format that the file will be saved as. The downside is what happens if the user then changes the file format (or indeed if one format file extension is just a lengthier version of a different format extension)? The other downside is that the text box and drop down list are both buried in the JFileChooser so are probably pretty difficult to get at programatically. So, actually, no let's just not do that.

The problem with a checkbox is that the only place this can appear is to the right of the folder view panel. That would look pretty awkward.
The "Inlcude backup files" checkbox appears here but underneath the "Recently opened files" panel, so doesn't look awkward. There is an argument for including the "Recently opened files" panel in the "Save as" dialog (e.g. selecting a recently used folder, or indeed overwriting files), so I would propose adding the Recently opened files panel, and the "Select format from extension" underneath that to the "Save as" file chooser dialog.