Use modified IntegerTreeNode... Test output ->
class rather than a new one. Makes no sense to produce a
seperate set version as most of it is the same. Instead
simply have an addSet method for set versus list.

-> Test output remains the same:

$ java TestIntSets
Run tests on TreeIntSet:
add 7 to the set
add 9 to the set
add 7 to the set again!
print the set contents: 7, 9
verbose test whether set contains 9:
	contains checks 9 against 7
	contains checks 9 against 9
	Result set does contain 9
extend set to: 7, 3, 1, 9, 8, 49, 13, 29, 22, 21, 19, 14, 18, 23, 27, 26, 45, 35, 34, 33, 37, 41, 39, 43, 44, 50
verbose test whether set contains 19:
	contains checks 19 against 7
	contains checks 19 against 9
	contains checks 19 against 49
	contains checks 19 against 13
	contains checks 19 against 29
	contains checks 19 against 22
	contains checks 19 against 21
	contains checks 19 against 19
	Result set does contain 19
verbose test whether set contains 28:
	contains checks 28 against 7
	contains checks 28 against 9
	contains checks 28 against 49
	contains checks 28 against 13
	contains checks 28 against 29
	contains checks 28 against 22
	contains checks 28 against 23
	contains checks 28 against 27
	Result set does not contain 28

Re-Run the same tests on ListIntSet:
add 7 to the set
add 9 to the set
add 7 to the set again!
print the set contents: 7, 9
verbose test whether set contains 9:
	contains checks 9 against 7
	contains checks 9 against 9
	Result set does contain 9
extend set to: 7, 9, 3, 49, 13, 29, 45, 35, 34, 22, 23, 37, 21, 27, 41, 43, 19, 26, 8, 14, 50, 1, 33, 39, 18, 44
verbose test whether set contains 19:
	contains checks 19 against 7
	contains checks 19 against 9
	contains checks 19 against 3
	contains checks 19 against 49
	contains checks 19 against 13
	contains checks 19 against 29
	contains checks 19 against 45
	contains checks 19 against 35
	contains checks 19 against 34
	contains checks 19 against 22
	contains checks 19 against 23
	contains checks 19 against 37
	contains checks 19 against 21
	contains checks 19 against 27
	contains checks 19 against 41
	contains checks 19 against 43
	contains checks 19 against 19
	Result set does contain 19
verbose test whether set contains 28:
	contains checks 28 against 7
	contains checks 28 against 9
	contains checks 28 against 3
	contains checks 28 against 49
	contains checks 28 against 13
	contains checks 28 against 29
	contains checks 28 against 45
	contains checks 28 against 35
	contains checks 28 against 34
	contains checks 28 against 22
	contains checks 28 against 23
	contains checks 28 against 37
	contains checks 28 against 21
	contains checks 28 against 27
	contains checks 28 against 41
	contains checks 28 against 43
	contains checks 28 against 19
	contains checks 28 against 26
	contains checks 28 against 8
	contains checks 28 against 14
	contains checks 28 against 50
	contains checks 28 against 1
	contains checks 28 against 33
	contains checks 28 against 39
	contains checks 28 against 18
	contains checks 28 against 44
	Result set does not contain 28