test/bench revisions;

test/bench revisions;
  * reverse-complement: port C algorithm to Go
	saves 30% on my MacBook Pro and makes it a fairer comparison.
  * test reverse-complement with and without GC (another 15%)
  * revise timing.sh to work on more systems
  * avoid two glibcisms in fasta.c

R=r
https://golang.org/cl/156110