Changes to the diag mediator:

[nichannah]

    1. Renaming of 'diag' variable to 'diag_cs', to avoid confusion
       with a new diag type to be introduced.
    2. Support dynamically sized diagnostic array.
    3. Introduce a generalised concept of diagnostic 'variations'.
       Each primary diagnostic can have many variations or aliases
       that are registered and posted at the same time as the
       primary. An example of this is the CMOR diagnostics.

Closes #171

[adcroft]

Even with the fixed uninitialized variable I'm still getting a SEGV with all compilers for both global_ALE/layer and global_ALE/z. Unfortunately using a debug executable fixes the problem.

@nicjhan Can you try global_ALE/z yourself and see what you come up with?

[nichannah]

This one is ready now. I have also rebased onto the latest dev/master