O(1) list and sequence operations

[mahrud]

Here is an example of a simple operation involving lists and sequences which should really be an O(1) operation. There are many others like it.

i1 : elapsedTime(10^8:0);
 -- 0.466494 seconds elapsed
---
i1 : elapsedTime toList toSequence toList(10^8:0);
 -- 2.20352 seconds elapsed

Related: #1608, #1904, #1978