manifests: push down expected node length into the parser
This strictly enforces the node length in the manifest lines according
to what the repository expects. One test case moves large hash testing
into the non-treemanifest part as treemanifests don't provide an
interface for overriding just the node length for now.
Differential Revision: https://phab.mercurial-scm.org/D10533
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..