goom: fix undefined behaviour of left-shift

Don't left-shift into the sign bit, the result is undefined and potentially
an overflow could flip the sign.
goom: fix compilation on ios-arm7-10.9 and osx-x86_64

uint is not a standard type, and the rest of the code uses
Uint which is locally typedefed to unsigned int.

https://bugzilla.gnome.org/show_bug.cgi?id=729067
goom: Remove french comment saying to prefix functions

All non-static function in this file are already prefixed with goom_.