Support SMPTE as input for 'time' fields when unit is set for the scene

You can do 1h3s4
Or to use smpte directly: 1:0:3:4

More on SMPTE:
http://en.wikipedia.org/wiki/SMPTE_timecode

* Support SMPTE display when entering a button

* Add parser to remove leading 0 from smtpe (because blender doesn't understand leading 0)
01:02:03  --> 1m2s3

* Add a time unit 'frame' that does not apply any scaling factor
(values entered in the UI are left unchanged)

* Added a B_UNIT_DEF_NOSCALE flag to bypass scaling.