Use pixman's release package instead of git

[davidgfnet]

Fixes the non-standard directory naming. Also removes the usage of autogen.sh script, which seems to cause some issues on mismatching autoreconf versions. Most distros seem to use the freedesktop release archive too.

[fjtrujy]

If you don't change the version I think you need to increase the package number

[davidgfnet]

Oopsie! Well spotted! Gracias!

[sharkwouter]

Thanks!