Update release notes for 1.15
Update release notes for 1.15
Merge branch 'wm-notes-1.15.0' of https://github.com/rethinkdb/rethinkdb into wm-notes-1.15.0

Conflicts:
	NOTES.md
Add missing PR
Add a few newly-closed issues
Fix version number
Backtrace should prefix geo terms
Fix errant edit
Updates based on comments
More updates, two new issues
Change release name
Move special case for r.table* in 'can_prefix'
Change 'update' to 'replace'
Clarify "upgrading" tables
Fix for can_prefix in case args is not an array
Don't permit object-like operations on ptypes
Thread checks in where it makes sense.
Test merge arguments too
Insert checks for merge arguments
Test path arguments