BUG: incorrect default in df.convert_objects was converting object types in applymap (#2909)

DOC: typos in RELEASE.rst
Merge pull request #2910 from pydata/applymap

BUG: incorrect default in df.convert_objects was converting object types (#2909)
BUG: support data column indexers that have a large numbers of values
     'in' the columns/index (and are not in the index/column) and
     not simple criteria

DOC: update release notes

CLN: cleanup indexing code for field indexer