When a branch is specified to check out in clone, update the remote tracking `HEAD` to point to it. This mimics git's behavior, when `git clone -b <name>` is used.
Update `refs/remotes/origin/HEAD` as a symbolic link to the remote's default branch.
We derive the branch name, even in our code, we shouldn't assume that the branch will be "master".
When cloning an empty repository, we need to guess what the branch structure should be; instead of hardcoding `master`, use the `init.defaultBranch` setting it if it provided.
When compiling libgit2 with -DDEPRECATE_HARD, we add a preprocessor definition `GIT_DEPRECATE_HARD` which causes the "git2/deprecated.h" header to be empty. As a result, no function declarations are made available to callers, but the implementations are still available to link against. This has the problem that function declarations also aren't visible to the implementations, meaning that the symbol's visibility will not be set up correctly. As a result, the resulting library may not expose those deprecated symbols at all on some platforms and thus cause linking errors. Fix the issue by conditionally compiling deprecated functions, only. While it becomes impossible to link against such a library in case one uses deprecated functions, distributors of libgit2 aren't expected to pass -DDEPRECATE_HARD anyway. Instead, users of libgit2 should manually define GIT_DEPRECATE_HARD to hide deprecated functions. Using "real" hard deprecation still makes sense in the context of CI to test we don't use deprecated symbols ourselves and in case a dependant uses libgit2 in a vendored way and knows it won't ever use any of the deprecated symbols anyway.
Our file utils functions all have a "futils" prefix, e.g. `git_futils_touch`. One would thus naturally guess that their definitions and implementation would live in files "futils.h" and "futils.c", respectively, but in fact they live in "fileops.h". Rename the files to match expectations.
In libgit2 nomenclature, when we need to verb a direct object, we name a function `git_directobject_verb`. Thus, if we need to init an options structure named `git_foo_options`, then the name of the function that does that should be `git_foo_options_init`. The previous names of `git_foo_init_options` is close - it _sounds_ as if it's initializing the options of a `foo`, but in fact `git_foo_options` is its own noun that should be respected. Deprecate the old names; they'll now call directly to the new ones.