Add trackback/pingback/comment differentiation to wp_notify_moderator()

[Otto42]

On the support forums, people often complain about how comments keep coming even though they're "turned off". Usually these end up being pingbacks or trackbacks, as that's how almost all comment spam is sent these days.

It would be nice if the moderation email made a distinction between comments and other stuff in the same way that the other emails already do.

Patch attached to do just that.

[Otto42]

Adds pingback/trackback identifier to moderation emails

[westi]

(In [6873]) More specific moderation emails for {ping|track}backs. Fixes #4986 props Otto42.