templatekw: add p1rev, p1node, p2rev, p2node keywords The {parents} template is cumbersome for some uses, as it does not show anything if there's only one "natural" parent and you can't use it to get the full 40 digit node hashes for parents unless you rely on the behavior of the --debug flag. Introduce four new template keywords: {p1rev}, {p2rev}, {p1node} and {p2node}. The "node" flavors of these always show full 40 digit hashes, but users can get the short version with a filter construction like '{p1node|short}'.