Allow to specify filenames according to requests lib format
Allow to specify filenames according to requests lib format

Allow to specify tuple `('filename.xls', open('filename.xls'))` for 'upload' or any other field.

Right now using `upload: open('filename.xls')` ckan won't receive the filename which will result in dummy 'upload' file, ie. http://localhost:5000/dataset/1b469259-02e2-43fa-864a-bf018eeef059/resource/799fb449-6249-4ea6-8ddd-24550b5b8dba/download/upload
xingyz/ckanapi,wardi/ckanapi,metaodi/ckanapi,perceptron-XYZ/ckanapi,LaurentGoderre/ckanapi,eawag-rdm/ckanapi