Document the installation and packaging of gitwrapper for -portable

Rather than hard-code assumptions into gitwrapper and gotd binaries, allow for some values to be overriden at compile time. This should help portability.

Reads (git clone) are working but writes (git push) run into an error

Define a standard path to where git stores its libexec helpers. This is always going to be hit-and-miss hard-coded like this, but will suffice for now. Tested on ubuntu 22.04

This is needed for gitwrapper which will fail if its program name cannot be detected properly.

Bring gotd and gitwrapper closer to how libraries are detected.

Include listen.c; make it portable.

This builds gotctl, for the moment via --enable-gotd

When building gotd, also build gotsh.

This enables gotd -- for now, this is opt-in at compile-time, via: ./configure --enable-gotd

This restores the traditional diff -p behaviour in Got.

Some people are eager to try to make Got work just like Git by overlaying the repository and work tree. This causes problems with unveil conflicts at run-time. Fail as early as possible during 'got checkout' when users attempt this. cosmetic tweaks + ok op@

Based on a patch by gonzalo@ ok op@

If a locally added file in A status gets deleted from disk it will move into missing ! status. If the user then decides to delete the file we must remove the file index entry immediately rather than flagging the file for removal during the next commit operation. The file was never committed and lacks a base-blob and base-commit, so it cannot be removed during the next commit. As a result the commit operation was reporting a bogus "out of date" error. Found while diagnosing a related bug reported by gonzalo@ ok op@

If creating the /tmp display diff for a commitable item failed we would free the commitable item while it was already on the path list. Later on when the path list was freed in got_worktree_commit() a double-free would be detected and the program would be aborted. Found by gonzalo@ ok op@

This prevents gotd from closing the client connection before ref-update status reports have been sent. Seen while testing gotd on Linux, though I see no obvious reason why this race would not trigger on OpenBSD.

The limit commit queue is invariably filled with different commits to the queue containing all commits, so the index of the work tree's base commit in the real queue corresponds to a different commit in the limit queue. As such, the marker is drawn on an incorrect commit. Rather than fix this to draw the marker on the correct commit if it happens to be in the limit queue, don't draw the marker at all in limit view. As pointed out by Mikhail on the list, this information is not wanted in the limit view. Patch and report by Mikhail.