One of the problems with the FileChooser compared to the old file selector is
that it is difficult to search for files in the file chooser. Often typeahead is
not enough. E.g. if you have 100 files with the names
a-long-and-complicated-image-iteration-%d.pgm where %d is a running index. With
the file chooser you could write "*42*" to get the 42nd image, but there is no
easy way of doing the same in the file chooser.

To solve this I propose introducing of a search bar similar to the one used when
pressing Ctrl-g in Mozilla Firefox. Similarly the gtkfilechooser should when
ctrl-g is pressed open up a search widget at the bottom of the filechooser with
the following contents:

[x] Search: [..............] (v)Next (^) Prev [ ] Match case [ ] Filter

Where [x],(v),(^) are buttons
      [...] is an entry widget
      [ ] are check boxes

The behaviour should be mapped on the behaviour of FireFox. In addition the [ ]
Filter button can be used to show only a subset of the files in the file chooser.

E.g. to only show all pdf files, the user can press the combination Ctrl-g,
"*.pdf", and turn on Filter. 

Pressing [x] turns of the filtering.