sanitize time zones in DB and R

[balazsdukai]

Currently POSIXct class is used, because of the ltraj compatibility. But accurately tracking time zones in the database and in R is important. See

> t1 <- as.POSIXct(strptime("2003-06-01", "%Y-%m-%d", tz = "Europe/Paris"))
> attributes(t1)
$class
[1] "POSIXct" "POSIXt" 

$tzone
[1] "Europe/Paris"

> t1 <- as.POSIXlt(strptime("2003-06-01", "%Y-%m-%d", tz = "Europe/Paris"))
> attributes(t1)
$names
 [1] "sec"    "min"    "hour"   "mday"   "mon"    "year"   "wday"   "yday"   "isdst"  "zone"   "gmtoff"

$class
[1] "POSIXlt" "POSIXt" 

$tzone
[1] "Europe/Paris" "CET"          "CEST"