help: commands supporting --git point to the gitdiffs topic (issue1352)

mq: reflow qnew help, add help for options

hgweb: descend empty directories in web view When a manifest has a series of directories with nothing in them but a single directory, displaying the entire chain of empty directories allows for navigation down to the first non-empty directory with a single click. Because Java links package hierarchy to directory hierarchy, and because Java conventions include at least three empty directories at the top of this hierarchy, descending down empty directories is very common in Java web tools.