[r=dave-cheney] Fix build error with Go 1.3
[r=dave-cheney] Fix build error with Go 1.3

A change that landed in Go 1.3 was an additional restriction that you could not `go install` a package if there was no source to install. Prior to this the results of doing `go install launchpad.net/juju-core` were in consistent. If you did `go install launchpad.net/juju-core/...` then the base package would fail to build, but all the sub packages would build. In Go < 1.3 this was a warning. This failure is not an error and the whole `go install` command will return exit 1.

To fix this, as well as have a nice high level description that shows up in godoc.org, add a small file at the top level so it can be built (ie, a .a file is generated) which keeps the tool happy. It is worth noting that our hacked version of the Go 1.2 build tool for ppc64el also suffers from this limitation as it is a mash up of bits of Go 1.2 and Go 1.3's build tool.

nb. Why is there no source to install ? Because the only files in that directory end in _test.go; they are test source, not package source, and test source is never installed.

https://codereview.appspot.com/100580045/
tsakas/juju,bac/juju,wwitzel3/juju,jrwren/juju,mikemccracken/juju,macgreagoir/juju,sinzui/juju,reedobrien/juju,rogpeppe/juju,kat-co/juju,voidspace/juju,cloud-green/juju,anastasiamac/juju,mjs/juju,thomnico/juju,kat-co/juju,marcmolla/juju,tasdomas/juju,anastasiamac/juju,wwitzel3/juju,davecheney/juju,ericsnowcurrently/juju,gabriel-samfira/juju,mattyw/juju,mikemccracken/juju,howbazaar/juju,alesstimec/juju,alesstimec/juju,mjs/juju,fwereade/juju,frankban/juju,dooferlad/juju,marcmolla/juju,mhilton/juju,tych0/juju,perrito666/juju,gabriel-samfira/juju,tsakas/juju,tych0/juju,frankban/juju,alesstimec/juju,Altoros/juju-vmware,rogpeppe/juju,frankban/juju-tmp,wwitzel3/juju,tasdomas/juju,cloud-green/juju,frankban/juju-tmp,cloud-green/juju,mjs/juju,tsakas/juju,frobware/juju,bogdanteleaga/juju,frankban/juju-tmp,tych0/juju,marcoceppi/juju,dooferlad/juju,marcmolla/juju,macgreagoir/juju,perrito666/juju,dooferlad/juju,mjs/juju,reedobrien/juju,gabriel-samfira/juju,fwereade/juju,kat-co/juju,mhilton/juju-juju,mhilton/juju-juju,jrwren/juju,kat-co/juju,cherylj/juju,mhilton/juju,howbazaar/juju,marcmolla/juju,macgreagoir/juju,bac/juju,makyo/juju,howbazaar/juju,voidspace/juju,mattyw/juju,waigani/juju,tasdomas/juju,bz2/juju,tsakas/juju,voidspace/juju,Altoros/juju-cloudsigma,macgreagoir/juju,davecheney/juju,ericsnowcurrently/juju,AdamIsrael/juju,marcoceppi/juju,axw/juju,AdamIsrael/juju,mikemccracken/juju,bz2/juju,Altoros/juju-vmware,kat-co/juju,axw/juju,anastasiamac/juju,mikemccracken/juju,reedobrien/juju,sinzui/juju,axw/juju,bac/juju,thomnico/juju,frankban/juju,mhilton/juju-juju,bogdanteleaga/juju,axw/juju,gabriel-samfira/juju,tasdomas/juju,Altoros/juju-cloudsigma,sinzui/juju,makyo/juju,axw/juju,cmars/juju,mjs/juju,cherylj/juju,wwitzel3/juju,bz2/juju,cmars/juju,marcmolla/juju,alesstimec/juju,reedobrien/juju,mjs/juju,marcoceppi/juju,mattyw/juju,cloud-green/juju,bz2/juju,cherylj/juju,mjs/juju,marcoceppi/juju,anastasiamac/juju,Altoros/juju-cloudsigma,makyo/juju,voidspace/juju,bogdanteleaga/juju,bogdanteleaga/juju,dooferlad/juju,bac/juju,AdamIsrael/juju,dooferlad/juju,dimitern/juju,mhilton/juju-juju,fwereade/juju,Altoros/juju-vmware,tych0/juju,cmars/juju,dimitern/juju,davecheney/juju,dimitern/juju,mhilton/juju,sinzui/juju,alesstimec/juju,gabriel-samfira/juju,waigani/juju,frankban/juju-tmp,davecheney/juju,reedobrien/juju,perrito666/juju,dimitern/juju,frankban/juju,mhilton/juju,bac/juju,ericsnowcurrently/juju,cherylj/juju,bz2/juju,ericsnowcurrently/juju,dimitern/juju,frobware/juju,Altoros/juju-cloudsigma,rogpeppe/juju,perrito666/juju,Altoros/juju-vmware,makyo/juju,cmars/juju,mikemccracken/juju,anastasiamac/juju,waigani/juju,howbazaar/juju,frobware/juju,frankban/juju,mattyw/juju,ericsnowcurrently/juju,macgreagoir/juju,waigani/juju,AdamIsrael/juju,thomnico/juju,howbazaar/juju,thomnico/juju,jrwren/juju,fwereade/juju,perrito666/juju