The test coverage for ambiguous OIDs was pretty thin. This adds
a bunch of new objects both in packs, across packs, and loose that
match to 8 characters so that we can test various cases of
ambiguous lookups.
Without this change, any failed assertion in the second (or a later) test
inside a test suite has a chance of double deleting memory, resulting in
a heap corruption. See #1096 for details.
This leaves alone the test cases where we "just" use cl_git_sandbox_init()
and cl_git_sandbox_cleanup(). These methods already take good care to not
double delete a repository.
Fixes#1096
