parse_date_time: orders mdy/Y don't play well with dby/Y

[Henrik-P]

When using orders mdy or mdY together with dby or dbY in parse_date_time, the mdy and mdY formats are incorrectly parsed as dmy or dmY. For some reason mdy and dbY works though.

In all examples below, the mdy or mdY dates should be parsed as "2017-09-01" (Ymd).

Does not work:

# mdy & dby
parse_date_time(c("09-01-17", "02-Sep-17"), orders = c("mdy", "dby"), locale = "eng")
# [1] "2017-01-09 UTC" "2017-09-02 UTC"

# mdY & dby/Y
parse_date_time(c("09-01-2017", "02-Sep-17"), orders = c("mdY", "dby"), locale = "eng")
parse_date_time(c("09-01-2017", "02-Sep-2017"), orders = c("mdY", "dbY"), locale = "eng")
# [1] "2017-01-09 UTC" "2017-09-02 UTC"

# mdy/Y & dby/Y, with no mdy/Y in x 
parse_date_time("09-01-17", orders = c("mdy", "dby", "dbY"), locale = "eng")
parse_date_time("09-01-2017", orders = c("mdY", "dby", "dbY"), locale = "eng")
# [1] "2017-01-09 UTC"

---

Works:

# mdy vs dbY
parse_date_time(c("09-01-17", "02-Sep-2017"), orders = c("mdy", "dbY"), locale = "eng")

# ymd/Ymd vs dbY
parse_date_time(c("17-09-01", "02-Sep-2017"), orders = c("ymd", "dbY"), locale = "eng")
parse_date_time(c("2017-09-01", "02-Sep-2017"), orders = c("Ymd", "dbY"), locale = "eng")

# dmy/dmY vs dbY 
parse_date_time(c("01-09-17", "02-Sep-2017"), orders = c("dmy", "dbY"), locale = "eng")
parse_date_time(c("01-09-2017", "02-Sep-2017"), orders = c("dmY", "dbY"), locale = "eng")

[vspinu]

This happens because "b" format matches numeric months. This is not intended.