Introduced a alternated interface to rrd_graph using rrd_info style return

Introduced a alternated interface to rrd_graph using rrd_info style return
values: rrd_graph_v The graph_v interface returnes additional information
about the graph including the location of the graphing area within the
image. When called with '-' as filename it will even return the image data.
The new interface is supported in the rrdtool command line, RRDs perl and
ruby bindings.

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1331 a5681a0c-68f1-0310-ab6d-d61299d08faa