BUG: Bug in concatenation with duplicate columns across dtypes not merging with axis=0 (GH4771)
TST: Bug in iloc with a slice index failing (GH4771)
TST: add append/join tests for merging dup columns
BUG: join on dup columns (internally) failing
Merge pull request #4772 from jreback/concat_dups

BUG: Bug in concatenation with duplicate columns across dtypes not merging with axis=0 (GH4771)