add fallback support to dumb http servers

Currently, bower does not support dumb http servers.

```
bower install http://foobar.com/foobar.git
bower foobar#*       not-cached http://foobar.com/foobar.git#*      
bower foobar#*          resolve http://foobar.com/foobar.git#*      
bower foobar#*         checkout master                                           
bower foobar#*          ECMDERR Failed to execute "git clone http://foobar.com/foobar.git -b master --progress . --depth 1", exit code of #128    
```

There is already a mechanism in place to support a fallback to not use depth, it just isn't catching this case.

The entire err.details for this case is

```
Cloning into \'.\'...\nfatal: dumb http transport does not support --depth\n
```

I tried to keep the addition as brief as possible, assuming that any err that includes the string `--depth` most likely does not support it.