Inform user when push does nothing

[hdpoliveira]

Today, when a push operation does nothing, we do not inform the user.
This enhancement is for displaying an info message saying the push did not push anything.

Mercurial prints this on this situation:

PS > hg push     
pushing to C:\path\to\remote
searching for changes
no changes found

If there are secret changesets:

PS > hg push
pushing to C:\path\to\remote
searching for changes
no changes found (ignored 1 secret changesets)