Blender Git Loki

A number of improvements for the file output node(s).

1) Old CMP_NODE_OUTPUT_FILE and CMP_NODE_OUTPUT_MULTI_FILE have been merged,
only CMP_NODE_OUTPUT_FILE remains. All functions renamed accordingly.

2) do_versions code for converting single-file output nodes into multi-file
output nodes. If a Z buffer input is used, the node is made into a multilayer
exr with two inputs. (see below). Also re-identifies multi-file output nodes
with the CMP_NODE_OUTPUT_FILE type.

3) "Global" format is stored in node now. By default this overrides any
per-socket settings.

4) Multilayer EXR output implemented. When M.EXR format is selected for node
format, all socket format details are ignored. Socket names are used for layer
names.

5) Input buffer types are used as-is when possible, i.e. stored as B/W, RGB or
RGBA. In regular file output the format dictates the number of actual channels,
so the CompBuf is typechecked to the right type first. For multilayer EXR the
number of channels is more flexible, so an input buffer will store only the
channels it actually uses.

6) The editor socket type is updated from linked sockets as an indicator of the
actual data written to files. This may not be totally accurate for regular file
output though, due to restrictions of format setting.