fread colClasses support for POSIXct

[jangorecki]

Currently fread colClasses does not support conversion to POSIXct:

str(data.table::fread("c1,c2\n2018-01-31 03:16:57,b", colClasses=c(c1="POSIXct")))
#Classes 'data.table' and 'data.frame':	1 obs. of  2 variables:
# $ c1: chr "2018-01-31 03:16:57"
# $ c2: chr "b"
# - attr(*, ".internal.selfref")=<externalptr> 

related to #1450
once solved update: https://stackoverflow.com/questions/41903259/data-table-colclasses-conversion-to-posixct

[MichaelChirico]

Haven't quite closed the SO question since it refers to as.POSIXct being slow on huge data... Related to #587 or #1450 then?

[mattdowle]

Yes: #1450 outstanding.