lisa.datautils: Speedup and fix df_update_duplicates()
lisa.datautils: Speedup and fix df_update_duplicates()

FIX

Fix inplace=False behavior so that it does not modify the input.

Also speedup considerably the function by assuming most duplicated
values are not clustered. This is the common case and it avoids very
costly iteration of duplicated values.

ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa