rename kSuffix* to kAlgorithmIdentifier*
use kSuffixNone constant
annotate hashes throughout the system
replace FileChunk::kCasSuffix with shash::kSuffixPartial
rename shash::Digest<>::modifier to ::suffix
strongly type hash suffix

Conflicts:
	cvmfs/catalog_traversal.h
add crutch method MakePathWithSuffix(shash::Suffix)