Don't check if an unsigned value is negative

Error found by clang 3.2 on mingw.

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Add pragma to ignore the warning for clang also

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Use the "correct" syntax for pointer arithmetic

Found by clang 3.2 on mingw.

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>