Replacing cells with %load fails if the cells contain an additional new line

[hgrif]

A cell with

%load bla.py

Will give a FileNotFoundError: [Errno 2] No such file or directory: 'bla.py\n'.

On one hand, we might only want to have cells with a nice single line with %load. On the other hand, we often get feedback after a pipeline of 15 mins so it could be nice to be more lenient (and I don't know what will happen if you have a trailing whitespace). A .strip()here could save some hassle.