dirstate: change placeholder hash length to 20 bytes
Previously the new-node placeholder hash for manifests generated from the
dirstate was a 21byte long string of "!" characters. Normal hashes are only 20
bytes long. This makes it complicated to implement more efficient manifest
implementations which rely on the hashes being fixed length.
Let's change this hash to just be 20 bytes long, and rely on the astronomical
improbability of an actual hash being 20 "!" bytes in a row (just like we rely
on no hash ever being the nullid).
A future diff will do this for added and modified dirstate markers as well, so
we're putting the new newnodeid in node.py so there's a common place for these
placeholders.
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.