BUG Fix gridfield storing duplicate data in session
Merge pull request #3716 from tractorcow/pulls/3.1/fix-gridfield-session

BUG Fix gridfield storing duplicate data in session
ENHANCEMENT: Additional extension points for Tiny MCE editing, for when images are regenerated and manipulating the HTML prior to a save
Merge pull request #3721 from gordonbanderson/TINY_MCE_EDIT_EXTENSION_POINTS

ENHANCEMENT: Additional extension points when editing with Tiny MCE
FIX: GD - check file exists before getimagesize

Use is_readable to check the file exists and is readable
Merge pull request #3726 from willmorgan/bugfixes/gd-image-exists

FIX: GD - check file exists before getimagesize
Restructure of the docs markdown source files into more logical taxonomy.
Rebased on 3.1