git_merge_base() returns GIT_ENOTFOUND when it cannot find a merge
base. graph_desdendant_of() returns a boolean value (barring any
errors), so it needs to catch the NOTFOUND return value and convert it
into false, as not merge base means it cannot be a descendant.
I accidentally wrote a separate priority queue implementation when
I was working on file rename detection as part of the file hash
signature calculation code. To simplify licensing terms, I just
adapted that to a general purpose priority queue and replace the
old priority queue implementation that was borrowed from elsewhere.
This also removes parts of the COPYING document that no longer
apply to libgit2.
If commit timestamps are off, we're more likely to hit a traversal
where the first path ends up traversing past the root commit of the tree.
If that happens, it's possible that the loop will complete before the second
path marks some of those final parents. This fix keeps track of the root
nodes that are encountered in the traversal, and verify that they are
properly marked.
In the best case, with accurate timestamps, the traversal will continue
to terminate when all the commits are STALE (parents of a merge-base), as
it did before. In the worst case, where one path makes a complete traversal
past a root commit, we will continue the loop until the root commit itself
is marked.
`revwalk.h:commit_lookup()` -> `git_revwalk__commit_lookup()`
and make `git_commit_list_parse()` do real error checking that
the item in the list is an actual commit object. Also fixed an
apparent typo in a test name.
Moved it into graph.{c,h} which i created for the new "graph"
functions namespace. Also adjusted the function prototype
to use `size_t` and `const git_oid *`.
