gnuplot 5.0 incorrectly places group labels at the top of the graph

[derekbruening]

I already fixed an issue with gnuplot 5.0 due to its change from linetype to dashtype in 210e259.

Another issue remains: group labels, such as with clustered stacked graphs, are placed at the top of the figure. Looking at the cluster_stacked.perf test and sample, focusing on this label in the gnuplot:

set label "Private Caches" at 0.672000,0 center rotate by 0

With gnuplot 4.4.2 this becomes this line in the fig output:

4 1 -1 0 -1 -1 10 0.000 4 125 1050 2936 4774 Private Caches\001

With 5.0.x it has a 0 value for y:

4 1 -1 0 -1 -1 10 0.000 4 125 1050 2936 0 Private Caches\001

Investigations so far indicate a bug in gnuplot but the final culprit is not yet identified.