patman: Support collecting all lines in the commit message

patman: Support collecting all lines in the commit message

In some cases we want to collect all lines in the commit message so that
the commit can be recreated with the same message as before, or perhaps
with light filtering.

Add support for this.

Series-to: u-boot
Cover-letter:
patman: Minor improvements to prepare for series handling
This series includes a number of internal improvements to patman:
- Tidy-up of parsing
- Adjust how tests create the git tree
- Support for creating patches in a different git directory
- Faster determination of the upstream branch
- Ability to collect the body of a commit message as a series of lines
END

Signed-off-by: Simon Glass <sjg@chromium.org>