[Bf-codereview] Multi File Output Node (issue 5666047)

[lukas.toenne at googlemail.com]

Reviewers: bf-codereview_blender.org,

Description:
Adds a new node type for saving multiple image files from a single node.

Unlike the existing file output node this node has an arbitrary number
of possible input slots. It has a base path string that can be set to a
general base folder. Every input socket then uses its name as an
extension of the base path for file organization. This can include
further subfolders on top of the base path. Example:

Base path: '/home/user/myproject'
Input 1: 'Compo'
Input 2: 'Diffuse/'
Input 3: 'details/Normals'

would create output files
in /home/user/myproject: Compo0001.png, Compo0002.png, ...
in /home/user/myproject/Diffuse: 0001.png, 0002.png, ... (no filename
base given)
in /home/user/myproject/details: Normals0001.png, Normals0002.png, ...

Most settings for the node can be found in the sidebar (NKEY). New input
sockets can be added with the "Add Input" button. There is a list of
input sockets and below that the details for each socket can be changed,
including the sub-path and filename. Sockets can be removed here as
well. By default each socket uses the render settings file output
format, but each can use its own format if necessary.

To my knowledge this is the first node making use of such dynamic
sockets in trunk. So this is also a design test, other nodes might use
this in the future.

Adding operator buttons on top of a node is a bit unwieldy atm, because
all node operators generally work on selected and/or active node(s). The
operator button would therefore either have to make sure the node is
activated before the operator is called (block callback maybe?) OR it
has to store the node name (risky, weak reference). For now it is only
used in the sidebar, where only the active node's buttons are displayed.

Also adds a new struct_type value to bNodeSocket, in order to
distinguish different socket types with the same data type (file inputs
are SOCK_RGBA color sockets). Would be nicer to use data type only for
actual data evaluation, but used in too many places, this works ok for
now.

Please review this at http://codereview.appspot.com/5666047/

Affected files:
   source/blender/blenkernel/BKE_node.h
   source/blender/blenkernel/intern/node.c
   source/blender/blenloader/intern/writefile.c
   source/blender/editors/space_node/drawnode.c
   source/blender/editors/space_node/node_draw.c
   source/blender/editors/space_node/node_edit.c
   source/blender/editors/space_node/node_header.c
   source/blender/editors/space_node/node_intern.h
   source/blender/editors/space_node/node_ops.c
   source/blender/makesdna/DNA_node_types.h
   source/blender/makesrna/RNA_access.h
   source/blender/makesrna/intern/rna_nodetree.c
   source/blender/makesrna/intern/rna_nodetree_types.h
   source/blender/nodes/NOD_composite.h
   source/blender/nodes/composite/nodes/node_composite_outputFile.c