debugextensions: show ships-with-hg-core state as a separate field
This is less magical than rephrasing ships-with-hg-core as internal, and
we can distinguish "internal" liar. "tested with: internal" will be hidden
by the next patch.
test-debugextensions: add dummy extension to make ifcontains() test more solid
If testedwith were a string, ifcontains("3.2", testedwith) would match "3.2.1".
New test added to cover that.