The ownership semantics have been changed all over the library to be
consistent. There are no more "borrowed" or duplicated references.
Main changes:
- `git_repository_open2` and `3` have been dropped.
- Added setters and getters to hotswap all the repository owned
objects:
`git_repository_index`
`git_repository_set_index`
`git_repository_odb`
`git_repository_set_odb`
`git_repository_config`
`git_repository_set_config`
`git_repository_workdir`
`git_repository_set_workdir`
Now working directories/index files/ODBs and so on can be
hot-swapped after creating a repository and between operations.
- All these objects now have proper ownership semantics with
refcounting: they all require freeing after they are no longer
needed (the repository always keeps its internal reference).
- Repository open and initialization has been updated to keep in
mind the configuration files. Bare repositories are now always
detected, and a default config file is created on init.
- All the tests affected by these changes have been dropped from the
old test suite and ported to the new one.
