Blender Git Loki

ID Management: Improve speed of code used when creating/renaming and ID.

This alone can make e.g. adding 40k IDs with default name (i.e. 'fully
constant' case in table below) about 15-20% faster:

| Number and type of names of IDs | old code | new code | speed improvement |
| -------------------------------- | -------- | -------- | ----------------- |
| 40K, mixed (14k rand, 26k const) | 75s | 62s | 21% |
| 40K, fully random | 90s | 76s | 18% |
| 40K, fully constant | 94s | 77s | 22% |

Idea is to use a first pass, where we just check one item every nth ones,
until we have found the chunk in which we want to insert the new item,
then do a basic linear comparison with all items in that chunk as before.

Also, list is now walked backward, as in most common 'massive insertion'
cases new ID's names have higher number, hence ends up towards the end of
the list.

This new sorting function can be between a few percents and 50% quicker than
original code, depending on various factors (like length of common parts of
ID names, whether new IDs should be added towards the end or not, how high
in numbering we are, etc.).

Note: another, full bisecting approach was also tried, which gives a massive
reduction of comparisons (from n items to log2(n)), but it only gave minor
improvements of speed from original fully linear code, while adding a fair
amount of complexity to the logic. Only case it was shining was the unlikely
'very long, almost similar ID names' case (since `strcasecmp()` is rather
costly then).