This makes it easier to pass connection-related options around (proxy & custom headers for now). This fixes a bug in git_push_finish, which didn't reuse the provided proxy if the connection closed between the call to `git_remote_push` and the finish step.
Next to including several files, our "common.h" header also declares various macros which are then used throughout the project. As such, we have to make sure to always include this file first in all implementation files. Otherwise, we might encounter problems or even silent behavioural differences due to macros or defines not being defined as they should be. So in fact, our header and implementation files should make sure to always include "common.h" first. This commit does so by establishing a common include pattern. Header files inside of "src" will now always include "common.h" as its first other file, separated by a newline from all the other includes to make it stand out as special. There are two cases for the implementation files. If they do have a matching header file, they will always include this one first, leading to "common.h" being transitively included as first file. If they do not have a matching header file, they instead include "common.h" as first file themselves. This fixes the outlined problems and will become our standard practice for header and source files inside of the "src/" from now on.
Having the setting be different from calling its actions was not a great idea and made for the sake of the wrong convenience. Instead of that, accept either fetch options, push options or the callbacks when dealing with the remote. The fetch options are currently only the callbacks, but more options will be moved from setters and getters on the remote to the options. This does mean passing the same struct along the different functions but the typical use-case will only call git_remote_fetch() or git_remote_push() and so won't notice much difference.
The push object knows which remote it's associated with, and therefore does not need to keep its own copy of the callbacks stored in the remote. Remove the copy and simply access the callbacks struct within the remote.
It can be useful for the caller to know which update commands will be sent to the server before the packfile is pushed up. git does this via the pre-push hook. We don't have hooks, but as it adds introspection into what is happening, we can add a callback which performs the same function.
We always use "update by push".
The signature for the reflog is not something which changes dynamically. Almost all uses will be NULL, since we want for the repository's default identity to be used, making it noise. In order to allow for changing the identity, we instead provide git_repository_set_ident() and git_repository_ident() which allow a user to override the choice of signature.