git_oid_fromstrn: Simplify the implementation and fix memory access issues
blame: Fix compare function's data types

Previously the hunk_byfinalline_search_cmp function was called with different
data types (size_t and uint32_t) for the key argument but expected only the
former resulting in an invalid memory access when passed the latter on a 64 bit
machine.

The following patch makes sure that the function is called and works with the
same type (size_t).