pour liquids into containers on ground

Pour some liquid from inventory to near tile with *containers*.

* Old behaviour: liquid pours on ground.

* New behaviour:
![pour](https://cloud.githubusercontent.com/assets/6351438/3560592/a6fd3758-0978-11e4-88db-05ca3879d187.png)

upd: interface and behaviour changed. Look in comments for info.
Only for style: there is no need to add a level of indentation to this block, instead:
```
if(cont == NULL || cont->is_null()) {
    cont = inv_map_for_liquid(liquid, text, on_ground);
}

...old code here remains unchanged...
if(cont == NULL || cont->is_null()) {
```