Don't ping yourself, especially on localhost

[wonderboymusic]

This may just be a conversation starter, but I know these things to be true:

1) there is duplicated code spread between pingback( ) and do_enclose( )
2) If your post contains a bunch of links to your own site, and you save your post in the admin, you will ended up with memory leaks all over the place / seg faults / etc when you get hammered by HEAD requests triggered by the immediate cron that is spawned by the post being saved
3) you probably don't need to trackback yourself anyways

I moved some dupe code into functions and added some checks so we don't ping ourself when saving

for self-pings see #5224 and #14811

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