Alias holding railing -> hand on railing

BUR #7183 has been approved by @nonamethanks.

create alias holding_railing -> hand_on_railing

forum #196527
It's also stupid, that the "holding railing" wiki says, that you should not use the tag "holding" with it.

Guaro said:

It's also stupid, that the "holding railing" wiki says, that you should not use the tag "holding" with it.

That was me, I didn't know we had hand_on_railing and we have holding_* tags for other things we don't use holding for, like parts of someone's body.

That explains it. I wouldn't have been surprised if it were an old stupid wiki rule.

The bulk update request #7183 (forum #196531) has been approved by @nonamethanks.