\ is lost in post revisions

[hailin]

\ \add \sub etc in either title or content is lost in post revisions, and when restore from post revisions.

It's easy to test, eg, with the following simple post
title: test \
Content: hello \ and \add
\ is lost in every revision, and when restore from revision.

This creates big problems as many math expressions such as LaTeX
contains \ Many keywords begin with \
For example: \add \sub \multiple \left \right

The root cause is that wp_insert_post stripslahses, assuming slashes are added to the input. This is not the case when we read data from db. The fix I proposed here identified two such places and fixed this above issue.

patch

I want to thank Ryan for the discussion and suggesting fix for the first case.

(In [10620]) Escape before passing to insert/update post. Props hailin. fixes #9199 for trunk