Add a pointer to "hg -v help" to the bottom of hg help {,cmd} output
This should make it easier to discover global options.
As a bonus, they are no longer displayed by something like a
hg -v help dates
% file replaced with directory
adding a
% should fail - would corrupt dirstate
abort: file named 'a' already in dirstate
% directory replaced with file
adding a/a
% should fail - would corrupt dirstate
abort: directory named 'a' already in dirstate
% directory replaced with file
adding b/c/d
% should fail - would corrupt dirstate
abort: directory named 'b' already in dirstate