Doing away with “unknown timezone” warnings
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Timezone stuff can really drive you NUTS
– at least if you’re sitting in front of a German Windows-Box 
This is what I used to do to set my tz:
options(tz="Europe/Berlin")
And I always wondered why R would throw “unknown timezone” warnings:
> t <- "2011-11-08 09:42:00"
> as.POSIXct(t, tz=getOption("tz"))
[1] "2011-11-08 09:42:00 CET"
Warning messages:
1: In strptime(xx, f <- "%Y-%m-%d %H:%M:%OS", tz = tz) :
unknown timezone 'MET-1MST'
2: In as.POSIXct.POSIXlt(x) : unknown timezone 'MET-1MST'
3: In strptime(x, f, tz = tz) : unknown timezone 'MET-1MST'
4: In as.POSIXct.POSIXlt(as.POSIXlt(x, tz, ...), tz, ...) :
unknown timezone 'MET-1MST'
5: In as.POSIXlt.POSIXct(x, tz) : unknown timezone 'MET-1MST'
Someday I found out that setting tz via `options()` was not enough as the environment variable `TZ` is not affected and hence all the the trouble:
> Sys.getenv("TZ")
[1] "MET-1MST"
Changing this should do away with the nasty warnings:
> Sys.setenv(TZ="Europe/Berlin")
> Sys.getenv("TZ")
[1] "Europe/Berlin"
> as.POSIXct(t, tz=getOption("tz"))
[1] "2011-11-08 09:42:00 CET"
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