Bug 1561 - Bad code in clutter-alpha.c

The implementation of the easing modes equations followed closely
the JavaScript and ActionScript counterparts. Obviously, JS and AS
are not C-compatible, so later versions of gcc (4.4.0 for instance)
would complain about uninitialized variables and such. The code is
also obfuscated and hard to debug/understand.

For these reasons, the implementation should be unobfuscated and
sanitized.