Fix typo (uninitialized var)
NLA Eval Bugfix: Influence settings on active action didn't work

* The automatically calculated influence was overriding the value we were passing
  into the dummy strip, making this seem like it doesn't work

* Made some tweaks to prevent some potential memory-related bugs
   - nlastrips_ctime_get_strip() actually saves off references to the list of strips
     it gets, so declaring dummy_strip in an inner scope like this could potentially
     be quite dangerous
   - Prevented a potential memory leak for the early abort when there are no strips
     for whatever reason (it shouldn't occur though)
NLA Editor: Added dedicated icons for "pushdown" operator and for indicating the "tweaking" state

1) The "pushdown" operation is the actual name for the functionality
   previously represented by the snowflake. That is, pushing the active
   action onto the NLA stack as a new strip.

   The icon that is introduced here is the icon I originally wanted to
   use here for this purpose (but couldn't at the time the NLA was coded
   as we didn't have the master SVG available yet). I'm making this change
   now to hopefully make the "animation-layers" intentions behind the NLA
   design a lot clearer than they have been so far.

2) Also added a dedicated icon for representing that the active action
   is in the "tweaking" state (i.e. we're editing a particular strip's
   action). Previously we were abusing an icon designed for an entirely
   different purpose, mainly since its identifier looked like it would work.
NLA Editor: Display "tweaking action" status indicator icon in place of action-type icon

Instead of displaying the "tweaking action" status indicator icon on the right hand
side jammed against the mapping/no-mapping toggle (pin), this is now displayed as in
place of the action icon used on the left (as the type indicator). This is less messy
than the previous situation, which was needed partly due to the abuse of an unsuited
icon.
Code cleanup: Use enum instead of int in function signatures for bAnimChannelType settings callbacks
Fixes for errors uncovered after previous commit
Code cleanup: avoid int/uint mixup in cycles
Style cleanup: indentation, braces
Cycles: use LIKELY/UNLIKELY macros

Gives overall ~3% speedup in own tests for BMW scene.
Fix T40025: install_deps.sh generating wrong make flag for OSL

Most cases should be handled OK now (not all though, would make script way too much tricky -
bash is a hell of a messy language :/).
Cycles: avoid int->float conversions for pixel lookups

Gives ~3% speedup for image.blend test, and 6% for image heavy file.

Overall speedup in real-world use is likely much less.
Add check for LIKELY/UNLIKELY is CPU only
Fix T39928: Blender crash/freeze when game engine is started with animation played directly on camera object with parents.

Updating object IPOs is not currently thread-safe since it also updates
children. This leads to problems when parents and children are both
animated. For now, updating object IPOs is done in its own loop to avoid
threading issues.
NLA Editor Drawing: Set up AnimChannelType callbacks for drawing NLA Editor

This commit lays some of the groundwork needed to port the last of the NLA Editor
channel types that's still defined using custom code. By moving this code over
to the newer standardised framework, this will enable widgets to have tooltips
to make it easier for users to find out what various buttons do.

Currently this isn't hooked up to anything though.
NLA Editor: Second part of porting NLA Action channel to standard drawing system

This now works (barring one or two minor glitches and the operator on the pushdown
button being a bit of a hack). The old drawing code is still in place though, and
will be kept around for a little while yet while the last kinks are ironed out.
NLA Editor: Polishing a few rough edges with the cleanup
Code Cleanup: Remove old deprecated NLA channel drawing code
NLA Editor: Added dedicated operator for the pushdown operation
NLA Pushdown Operator: Active animdata option + More error handling

* If channel_index = -1, the pushdown operator will try to use the active AnimData
  block. To see which one this will be, check the properties (NKEY) region in NLA Editor.
* Added more detailed error handling for the various cases where things are not
  in a valid state for pushing down an action. This is notably to stop scripters
  from putting the NLA into an inconsistent state.
Code cleanup