openpgp: Add support for BZIP2-compressed data packets.
openpgp: Add support for BZIP2-compressed data packets.

Tested using a variety of files encrypted with gpg and the
"--compress-algo BZIP2" gpg option.

R=golang-dev, bradfitz, agl
CC=golang-dev
https://golang.org/cl/10801043

cheffo/crypto,ScriptRock/crypto,CodyGuo/crypto,bford/golang-x-crypto,guaiguaihw/crypto,progrium/crypto,bford/golang-x-crypto,cmars/tools,wooutl/golangcrypto,mattharden/crypto,thomaso-mirodin/crypto,thomaso-mirodin/crypto,pki-io/crypto,golang/crypto,guaiguaihw/crypto,zj8487/crypto,CodyGuo/crypto,kim-racktop/crypto,pki-io/crypto,lucevers/crypto,cmars/tools,golang/crypto,a-palchikov/crypto,Carrotman42/crypto,kim-racktop/crypto,a-palchikov/crypto,juniorz/crypto,wooutl/golangcrypto,mattharden/crypto,juniorz/crypto,cmars/tools,progrium/crypto,zj8487/crypto,conseweb/golangcrypto,tca/crypto,ScriptRock/crypto,tca/crypto,cmars/tools,cheffo/crypto,golang/crypto,Carrotman42/crypto,conseweb/golangcrypto,lucevers/crypto