Add the ability to use keywords in the backout, branch, checkout, cherrypick, and patch commands. Includes some basic regress tests for the new commands, and also some more contrived test cases for 'got log -c[:]keyword[:(+|-)[N]]'. ok stsp

ok jamsek

This begins enabling the use of keywords in got wherever commit ids or references are used, with more work intended to expand support across all such instances (e.g., branch, checkout, etc.), and add more keywords. The keywords ":base" and ":head" can be passed to 'got {diff,log,update} -c' commands as a substitute for the corresponding commit hash id. Keywords and references can also be modified by appending a ':+' or ':-' and an optional integer N to specify by first parent traversal the Nth generation descendant or antecedent, respectively. If N is omitted, a '1' is implicitly appended. tweaks + ok op and stsp

Also document that the commit/import/tag operations are aborted when the user fails to save the log message from the invoked editor. ok jamsek stsp

Don't make -C imply -c (a break statement was missing). Detect -an and -cn conflicts. Simplify by removing unneeded check for conflicting -aC (since -C requires -c, we can rely on the -ac conflict being detected). Update the man page to say -cC is allowed.

ok stsp@

ok op, james

When users run 'got add *' the shell may pick up already versioned files and trigger errors about paths being in an unexpected status. Expand the check which previously only allowed files in added status to be double-added to cover the following status codes which are all safe to ignore: A M C m This should make bulk additions of files a bit easier in most cases. Problem reported by robert@ ok jamsek

Split part of got_worktree_merge_prepare into a new function, got_worktree_merge_write_refs, since that part doesn't make sense in the fast-forward case. ok stsp@

Requested by James Cook

problem found by naddy@

Gap in the documentation pointed out by James Cook.

ed users are reading files with their minds rather then their eyes, and might therefore be missing important visual clues we write into files before the user gets to edit them. Use of vi(1) ensures that such clues will not be missed.