Fix candidates is empty on tmux

After I updated GVM to 1.3.0, candidates have been empty on tmux.

* zsh 5.0.2 (x86_64-apple-darwin12.2.0)
* tmux 1.8

On tmux:
```sh
% gvm help
...

   candidate  :
   version    :  where optional, defaults to latest stable if not provided

eg: gvm install groovy
```
```sh
% gvm list groovy

Stop! groovy is not a valid candidate.
```
```sh
% echo "GVM_CANDIDATES: $GVM_CANDIDATES"
GVM_CANDIDATES: 
```
```sh
% echo "GVM_CANDIDATES_CSV: $GVM_CANDIDATES_CSV"
GVM_CANDIDATES_CSV: 
```
```sh
% cat ~/.gvm/var/candidates
gradle,grails,griffon,groovy,groovyserv,lazybones,vertx
```

I changed `GVM_CANDIDATES_CSV` to export.
But, `GVM_CANDIDATES` can't export because it is array.
So, I extract the function from setting the array, and call it even if gvm has been initialized.