"filename" parameter doesn't do anything in get_map / get_googlemap

```
myMap <- ggmap::get_map(
location = c(-64.726720, 32.348871),
zoom = 16,
mesaging = TRUE,
source = "google",
maptype = "satellite",
crop = TRUE,
filename = "anylocation")
ggmap::ggmap(myMap)
```

I find that entering a location for filename doesn't cause the files to be downloaded to this location, they're still saved to /var (in my friends mac setup, and feasibly also in my linux setup but mine works and hers doesn't so I don't get an error message to confirm on mine).

Can anyone confirm this?

Start by reproducing the supplied get_map call with filename set, then inspect the get_map and get_googlemap entry points for how the filename and download directory are handled. Confirm the behavior on the affected platform; done means the requested filename controls where the downloaded map files are saved instead of /var.

Written by the indexing model from the issue text.