doc: use correct cross reference in help documentation
This patch fixes problems below:
- ":hg:" role should be followed by not '"' but '`'
- there is a help topic not "default-push" but "config.default-push"
histedit: show correct hash ID at verification error
node.short() on 'ha' in verifyactions() causes broken hash ID, because
it is initialized with node.hex()-ed node value.