need to compare the escaped levels for styleEqual()

[shrektan]

Closes #723

A minimal repro

library(DT)
tbl = data.frame(
  A = c('a', 'b', '>a', "<b"),
  B = c('red', 'green', 'yellow', 'pink'),
  stringsAsFactors = FALSE
)
datatable(tbl) %>% 
  formatStyle("A", target = "row", backgroundColor = styleEqual(tbl$A, tbl$B))

[yihui]

Thanks!

[hjia222]

@shrektan Thanks!