add pagesize param to constructor for SimplePageManager
make the MultiCursor constructor private
reworked combo class to use abstract class plus subclasses, and made it easier to create a multicursor with more than 2 subs.  added a test that merges ten segments at the same time and then verifies that the result is sorted properly.
ha!  the test suite passes with only one page per block.  absurd.
modified a test to read an overflowed value in small chunks, to make sure the OverflowReadStream implementations can handle that.