repository: Change ownership semantics

repository: Change ownership semantics

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.