The plain text renderer would normally render as text anything that's not binary.
However, there are a few formats (mainly PDF, RTF, etc.) that are not detected as binary, but not human readable either...
For the time being, we maintain a list of this kind of format which should be treated as binary.
Fixes #1920.
Authored by: cboos 2005-09-04
Parent: [r2178]
Child: [r2180]
