[Babel] [Ann] varied updates and improvements

["Eric Schulte" <schulte.eric@gmail.com>]

Hello Babblers,

I've just merged in a large group of changes to Babel (authored by Dan
and myself) including a couple of user-visible enhancements and a
significant cleanup of the code base.  More information is available in
the Changes.org file (relevant sections included below).

Best -- Eric

Incompatible Changes 
=====================

Code block hashes 
------------------
Due to changes in the code resolving code block header arguments
hashing of code block results should now re-run a code block when
an argument to the code block has changed.  As a result of this
change *all* code blocks with cached results will be re-run after
upgrading to the latest version.

Testing update 
---------------
Anyone using the org-mode test suite will need to update the jump
repository for test navigation by executing the following from
the root of the org-mode repository.
git submodule update
Failure to update this repository will cause loading of
org-test.el to throw errors.

Details 
========

Multi-line header arguments to code blocks 
-------------------------------------------
Code block header arguments can now span multiple lines using the
new =#+header:= or =#+headers:= lines preceding a code block or
nested in between the name and body of a named code block.
Examples are given below.

- multi-line header arguments on an un-named code block
  #+headers: :var data1=1
  #+begin_src emacs-lisp :var data2=2
    (message "data1:%S, data2:%S" data1 data2)
  #+end_src
  
  #+results:
  : data1:1, data2:2

- multi-line header arguments on a named code block
    #+source: named-block
    #+header: :var data=2
    #+begin_src emacs-lisp
      (message "data:%S" data)
    #+end_src
  
    #+results: named-block
    : data:2

Unified handling of variable expansion for code blocks 
-------------------------------------------------------
The code used to resolve variable references in code block header
arguments has now been consolidated.  This both simplifies the
code base (especially the language-specific files), and ensures
that the arguments to a code block will not be evaluated multiple
times.  This change should not be externally visible to the
Org-mode user.

Improved Caching 
-----------------
Code block caches now notice if the value of a variable argument
to the code block has changed, if this is the case the cache is
invalidated and the code block is re-run.  The following example
can provide intuition for the new behavior.

  #+srcname: random
  #+begin_src R :cache yes
  runif(1)
  #+end_src
  
  #+results[a2a72cd647ad44515fab62e144796432793d68e1]: random
  0.4659510825295
  
  #+srcname: caller
  #+begin_src emacs-lisp :var x=random :cache yes
  x
  #+end_src
  
  #+results[bec9c8724e397d5df3b696502df3ed7892fc4f5f]: caller
  0.254227238707244