Support check.names = FALSE in merge.xts()

[joshuaulrich]

merge.xts() does not currently honor check.names = FALSE. This is documented behavior, but it would be nice to have support.

x <- xts::.xts(1:3, 1:3, dimnames = list(NULL, "42"))
y <- xts::.xts(1:3, 1:3, dimnames = list(NULL, "21"))
merge(x, y)                       # leading "X" added
merge(x, y, check.names = TRUE)   # same
merge(x, y, check.names = FALSE)  # should have numeric column names