Wrong behavior of new command with vim v7.4

Following vader test shows a wrong behavior with vim 7.4:

```
Execute (Test new):
call vader#log("1 bufname " . bufname("%"))
silent execute "new toto/"
call vader#log("2 bufname " . bufname("%"))
silent execute "buffer toto/"
call vader#log("3 bufname " . bufname("%"))
```

I get the following output:
```
Starting Vader: 1 suite(s), 1 case(s)
Starting Vader: /tmp/test.vader
(1/1) [EXECUTE] Test new
> 1 bufname [Vader-workbench]
> 2 bufname [Vader-workbench]
> 3 bufname toto/
Success/Total: 1/1
```

but I expect this one:
```
Starting Vader: 1 suite(s), 1 case(s)
Starting Vader: /tmp/test.vader
(1/1) [EXECUTE] Test new
> 1 bufname [Vader-workbench]
> 3 bufname toto/
> 3 bufname toto/
Success/Total: 1/1
```

Two things to note:
* the culprit is the buffer name, finishing with a `/` (it is indeed a valid buffer name)
* it works with neovim, did not try with vim 8.0