Adapted graphic to work even if gdf fonts are missing + removal of some code for php < 4.3 compatibility

Signed-off-by: emanuele <emanuele45@gmail.com>
 Adapted the credits template to accomodate more categories of external stuff

Signed-off-by: emanuele <emanuele45@gmail.com>
Added a new set of fonts for the CAPTCHA

Signed-off-by: emanuele <emanuele45@gmail.com>
Merge pull request #330 from emanuele45/fonts

New set of fonts (SIL - OFL) and some other change to the captcha