With this patch and ":eval only-manual" in a babel header,

Org evaluates the source code if it is run via ~org-ctrl-c-ctrl-c~ (e.g. =C-c C-c= in the babel block), but not if run via the ~org-babel-execute-buffer~ function.

This is my first contribution to Org core. I've signed FSF papers. 

  -k.