Don't use '==' for equality matching in sh, as this won't work across all shells. ok @naddy

Since the interpreter for the regress shell scripts are using /bin/sh this will usually imply some level of POSIX compliance (that isn't bash-specific, for instance). Some systems use dash as their sh shell and as such is stricter POSIX compliance. To help -portable, make the shell test checks use a single '=' for equality, rather than '=='.

The letter "o" does not overlap with existing options of 'got ref' and is also used by mutt(1) for this purpose.

This fixes an issue where some references were missing from lists of references sorted by timestamp.

Move a small amount of code from worktree.c to a new file worktree_open.c, which contains everything required to open and close a work tree and inspect some of its basic parameters. This can be used by gotadmin. ok tracey

Replace hand-rolled parentheses with the proper mdoc(7) macro, otherwise the closing ")" ends up inside the command description. Reported by Josh Rickmar, thanks!

Always update to the specified branch even if the branch is already rebased (no commits needed to be rebased, and the branch does not need a fast forward). With the old behavior of erroring and staying on the current branch, I sometimes found myself ignoring the error message, treating it as information and assuming the branch update, and later on committing on top of origin/main instead of the main branch. feedback and ok stsp

Tests by kn, thomas_adam and myself made on various repositories indicate that 3 is a good choice. Tyring 10 deltas is much slower and does not result in significantly smaller pack files.