make Xor32Detector friends with the associated unit test
move T_ChunkDetectors test into upload namespace (friends requirement)
add unit test to check xor32 implementation
specify unsigned-ness for xor32 function
re-define chunking cut marks after portability fix
Merge pull request #304 from reneme/test_xor32

FIX: Portability of XOR32 Implementation To The ARM Platform

The xor32 implementation in the Xor32Detector was taking a char as input parameter. It turns out that the C standard does not define the 'signed-ness' of char leading to unportable code. (x86 interprets char as a signed char whereas ARM takes it as an unsigned char). This fixes this ambiguity by changing the input parameter of xor32 to unsigned char with the expense of a changed behaviour on x86.

Note: This already contains a fix to the directly affected unit tests but it breaks others as well.