Update release notes
Update release notes
Add bugs #3287 and #3205
Added bug #3259
Added #3300; fixed some style issues
Typo
Merge pull request #3291 from rethinkdb/watts-1.15.2-notes

Watts 1.15.2 notes
Bump Python driver to 1.15.0-2
Made us print details when groups is non-empty in failing RDBBtree unit test.
Made datum_string_t constructor not have undefined behavior (by not passing NULL to memcpy).
Made store_key_t::min not cause undefined behavior by passing NULL to memcpy.
Made datum_string_t constructor not create undefined behavior by passing NULL to memcpy.
Update serialization version to v1.16.
Merge branch 'sam_2042' into v1.15.x
Merge branch 'v1.15.x' into next

Conflicts:
	src/rdb_protocol/datum.cc
Merge branch 'v1.15.x' into sam_0_null_undefined
Merge branch 'sam_0_null_undefined' into v1.15.x
Merge branch 'v1.15.x' into next
Removed unused private field.
Fix errors introduced in previous commit.