They aren't much useful in Math namespace and here it allows to handle
also Color3/Color4 types. Moreover all RGBA component names were removed
from Math namespace, so it would be inconsistent to have them there only
in swizzle() functions.
CORRADE_GRACEFUL_ASSERT is set only on files where it makes sense, the
rest is shared between main and test libraries. Speeds up the
compilation like infinity times.
CMake 2.8.8 is required for OBJECT library target.