use is.object(x) instead of grepl("OBJ", .Internal(inspect(x))[1]) in tests

[BillDunlap]

reshape2/tests/testthat/test-melt.R uses an illegal-on-CRAN .Internal(inspect(x)) along with some ugliness to see if an item is an S4 object:

object_bit_set <- function(x) {
grepl("\[OBJ", capture.output(.Internal(inspect(x)))[1])
}
t.long <- melt(t.wide, measure.vars=c("t1", "t2", "t3"), value.name="time")
expect_true(object_bit_set(t.long$time))

I believe object_bit_set(x) is equivalent to is.object(x) and is.object is a core R function.