[contrib] New linearize format

The new linearize format outputs one month's worth of bitcoin transactions, as determined by the timestamp inside the block.  The file last-modified time is set to the highest timestamp seen thusfar in the processing:
```
-rw-rw-r-- 1 jgarzik jgarzik    512129 Sep 30  2009 blk00008.dat
-rw-rw-r-- 1 jgarzik jgarzik    522737 Oct 31  2009 blk00009.dat
-rw-rw-r-- 1 jgarzik jgarzik    521531 Nov 30  2009 blk00010.dat
-rw-rw-r-- 1 jgarzik jgarzik    992159 Dec 31  2009 blk00011.dat
-rw-rw-r-- 1 jgarzik jgarzik   1190943 Jan 31  2010 blk00012.dat
-rw-rw-r-- 1 jgarzik jgarzik   1580654 Feb 28  2010 blk00013.dat
-rw-rw-r-- 1 jgarzik jgarzik   1435103 Mar 31  2010 blk00014.dat
-rw-rw-r-- 1 jgarzik jgarzik   2646319 Apr 30  2010 blk00015.dat
-rw-rw-r-- 1 jgarzik jgarzik   2040834 May 31  2010 blk00016.dat
-rw-rw-r-- 1 jgarzik jgarzik   1911267 Jun 30  2010 blk00017.dat
-rw-rw-r-- 1 jgarzik jgarzik   7862024 Jul 31  2010 blk00018.dat
```

A check is added to verify that blocks remain in the proper order.  Previously this was guaranteed by bitcoind anyway, and so is a simply a sanity check.  ~~Who knows what weird input people might feed to this.~~  Headers-first will change this, sometimes storing blocks out of order on disk.  linearize will need a future update to buffer blocks.

This new format is suitable for researchers performing lots of raw block processing, and bitcoind users importing via "-reindex".  The reindex import method is superior to bootstrap.dat.

I think you meant month here (and maybe not _timestamp, but _month?)