added min_doc_count to HistogramAgg and DateHistogramAgg
added min_doc_count to HistogramAgg and DateHistogramAgg

Fiedzia/pyes,HackLinux/pyes,jayzeng/pyes,jayzeng/pyes,mavarick/pyes,haiwen/pyes,aparo/pyes,mavarick/pyes,haiwen/pyes,mavarick/pyes,aparo/pyes,Fiedzia/pyes,jayzeng/pyes,aparo/pyes,HackLinux/pyes,Fiedzia/pyes,haiwen/pyes,HackLinux/pyes