There is no assurance that all prefix codes are reachable as
optimal Huffman codes for the numbers of symbols encountered in
a deflate block. This code considers all possible prefix codes,
which might be a larger set than all possible Huffman codes,
depending on the constraints.
Also clean up comparisons between different types, and some odd
indentation problems that showed up somehow.
A new endless loop was introduced by the clang compiler, which
apparently does odd things when the right operand of << is equal to
or greater than the number of bits in the type. The C standard in
fact states that the behavior of << is undefined in that case. The
loop was rewritten to use single-bit shifts.
