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.

Same problem as fixed in 90de04bc7f1b85b9c491bcd124f6178fad005de1. ok stsp

Problem reported and fix tested by Omar Polo.

Explicitly cast "char" to "unsigned char" when assigned to "int" to prevent sign extension from breaking comparions against EOF or passing invalid arguments to ctype functions.