formulas don't work with brmsformula objects produced by `bf()`

We fail in a few places, including:

in validate_params_individually we have

assertthat::assert_that(
inherits(f_det, "formula"),
msg = formula_error("detection")
)

in is_flocker_formula we have

is_flocker_formula <- function (x) {
is_formula(x) & as.character(x)[1] == "~" & length(x) == 2
}

More importantly, inside flock_ we have things like

if (!is.null(f_occ)) {
    f_occ_txt <- paste0(deparse(f_occ), collapse = "")
    f_occ_use <- stats::as.formula(paste0("occ ", f_occ_txt))
  }

Can we come up with a slick fix?

jsocolar / flocker