"rrd_parsetime" uses (many) global variables and is thus not

thread-safe. Using it in the FETCH command reproducably segfaults the
caching daemon.

This replacement will only work with "simple" integers, i. e. times
specified as "1272470594" (sometime on April 28th) or "-3600" (one hour
ago). -- Florian Forster

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@2074 a5681a0c-68f1-0310-ab6d-d61299d08faa