Add checkEnvironment call into cmdHellInit before printExport.

[lalyos]

The same as cmdUp does: "Your environment variables are already set correctly." written to stderr in case no actions needed.
This way env correctness can be checked in a script by:

if [[ "$(boot2docker-cli shellinit 2>/dev/null)" == "" ]]; then
  # env is ok
else
  # env isn't correct
fi

[tianon]

Seems sane IMO; LGTM

cc @Moghedrin @gmlewis

[gmlewis]

So correct me if I'm wrong, but let's say someone starts up a new shell, and it is already configured properly... then the result of running $(boot2docker-cli shellinit) would be identical to running $(echo "") which appears to be benign.
If this is the case, then LGTM.

[lalyos]

@gmlewis To be precise $(boot2docker-cli shellinit 2>/dev/null) will be equal to $(echo "")

Its still writes to stderr

$ boot2docker-cli shellinit
Writing /Users/lpapp/.boot2docker/certs/boot2docker-vm/ca.pem
Writing /Users/lpapp/.boot2docker/certs/boot2docker-vm/cert.pem
Writing /Users/lpapp/.boot2docker/certs/boot2docker-vm/key.pem
Your environment variables are already set correctly.

[gmlewis]

LGTM. Merging.