Revision 1371114

LUCENE-3892: backporting r1371010 and r1371011 to BlockPacked.

I changed the comment on the value of BLOCK_SIZE. Indeed, since PackedInts
encoding/decoding is long-aligned, all numbers of bits per value that are
co-prime with 64 cannot encode/decode less than 64 values per iteration, so the
block size should be at least 64. Switching it to a lower value (eg. 32) should
work but will perform many unnecessary operations in the encoding/decoding step.