* add ability to find recipes in conda-recipes subfolders:

  * add ability to find recipes in anaconda_dir/conda-recipes subfolders: 
    with pre-check for ambiguities

I have put it in a separate function so that: main_build.py execute has not to be much changed

P

*output in case of ambiguities*
```
workerm@notebookpc:~/anaconda/bin$ ./conda-build appdirs 12_xtools-glibc

Multiple recipes with same name: <appdirs>
     /home/workerm/anaconda/conda-recipes/appdirs
     /home/workerm/anaconda/conda-recipes/Untitled Folder/appdirs
Ambiguities: specify full recipe path
workerm@notebookpc:~/anaconda/bin$ 

```