1) source blocks can now reference source-blocks in other files using
the filename:sourcename syntax
2) on export all references are now made to explicitly point to the
original buffer using the filename:sourcename syntax. This ensures
that all references are correctly resolved on export, even when the
referenced source block has already been processed.
And when merging header args, those from enclosing scopes take
precedence. For example, output to file from a source block is
implemented by (a) sending the output to file, and (b) having the
source block return the file name as its result. Before this change,
the file name returned could be set by a referenced source block (a
nested call), regardless of the value of the :file header arg of the
top-level source block.
Prior to this, reference resolution could fail with quoted
strings. E.g. this didn't work:
\#+srcname: py-id(a=1)
\#+begin_src python
a
\#+end_src
\#+lob: py-id(a="1")
