_PACKAGE sentinel does not work with roxygenise()

[krlmlr]

...only with devtools::document().

> roxygen2::roxygenise()
Error in asNamespace(ns, base.OK = FALSE) : not a namespace
16: stop("not a namespace")
15: asNamespace(ns, base.OK = FALSE)
14: getNamespaceInfo(ns, "path")
13: file.path(getNamespaceInfo(ns, "path"), "DESCRIPTION")
12: read.dcf(file, keep.white = "Authors@R") at description.R#3
11: read.description(file.path(getNamespaceInfo(ns, "path"), "DESCRIPTION")) at object-from-call.R#41
10: find_data_for_package(env) at object-from-call.R#28
9: find_data(call, env) at object-from-call.R#6
8: object_from_call(call, env, preref) at parse.R#34
7: (function (call, ref, comment_ref) 
   {
     ...
6: mapply(FUN = f, ..., SIMPLIFY = FALSE)
5: Map(extract, parsed, refs, comment_refs) at parse.R#39
4: FUN(X[[i]], ...)
3: lapply(package_files(base_path), parse_file, env = env) at parse.R#3
2: parse_package(base_path, load_code) at roxygenize.R#59
1: roxygen2::roxygenise()