lfs: prefetch lfs blobs when applying merge updates
In addition to merge, this method ultimately gets called by many commands:
- backout
- bisect
- clone
- fetch
- graft
- import (without --bypass)
- pull -u
- rebase
- strip
- share
- transplant
- unbundle
- update
Additionally, it's also called by histedit, shelve, unshelve, and split, but it
seems that the related blobs should always be available locally for these.
For `hg update`, it happens after the normal argument checking and pre-update
hook processing, and remote corruption is detected prior to manipulating the
working directory. Other commands could use this treatment (archive, cat,
revert, etc), but this covers so many of the frequently used bulk commands, it
seems like a good starting point.
Losing the verbose message that prints the file name before a corrupt blob
aborts the command is a little sad, because there's no easy way to go from oid
to file name. I'd like to change that message to list the file name so it looks
cleaner and less cryptic, but the pointer object is nowhere near where it needs
to be to do this. So punt on that for now.
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.