Default entry in org-src-block-faces

[Augusto Stoffel]

Would it make sense to allow a default entry (t FACE) in
`org-src-block-faces', to be applied to all src blocks without a more
specific entry in that alist?  There seems to be no other way to specify
a face to be applied to all src blocks, and only src blocks.

I also wanted to point out two minor issues in org-src.el:

- It refers to the `org-block' face without requiring `org-faces'.  This
  is probably never a problem in org itself, but if an external package
  loads `org-src' in order to fontify some code blocks, that face might
  be missing.

- The docstring of `org-src-block-faces' contains the word
  "respectability".