Tags: LukeShu/git

subtree: handle pointing it at a file

subtree: better replace fix

subtree: fix for older Bash

less strict

Merge branches 'lukeshu/to-upstream/signed-commits', 'lukeshu/to-upst…

…ream/tag-names-v2' and 'lukeshu/subtree-2021-04/everything' into lukeshu/next

fast-export, fast-import: implement signed-commits

fast-export has an existing --signed-tags= flag that controls how to
handle tag signatures.  However, there is no equivalent for commit
signatures; it just silently strips the signature out of the commit
(analogously to --signed-tags=strip).

While signatures are generally problematic for fast-export/fast-import
(because hashes are likely to change), if they're going to support tag
signatures, there's no reason to not also support commit signatures.

So, implement signed-commits.

On the fast-export side, try to be as much like signed-tags as possible,
in both implementation and in user-interface; with the exception that
the default should be `--signed-commits=strip` (compared to the default
`--signed-tags=abort`), in order to continue defaulting to the
historical behavior.  Only bother implementing "gpgsig", not
"gpgsig-sha256"; the existing signed-tag support doesn't implement
"gpgsig-sha256" either.

On the fast-import side, I'm not entirely sure that I got the ordering
correct between "gpgsig" and "encoding" when generating the commit
object.

Signed-off-by: Luke Shumaker <lukeshu@datawire.io>

subtree: Add a --notree flag