#708 set pointtype cycle
It is useful to be able to set the linetype and pointtype cycles to be relatively prime in order to maximize the number of distinct line+point combinations. For instance when plotting experimental results from trials done in 96-well plates it is an advantage to have all 96 curves easily distinguishable. Currently it is possible to adjust the repeat count of linetypes using "set linetype cycle N", but it is not possible to change the repeat count of point types (currently 15 for many terminals).
In practice I currently set the linetype cycle to 7, which gives me 7*15=105 distinct curves when plotting "with linespoints". This patch gives me the flexibility to use more colors but fewer point types, or to force the point type cycle to some known value on terminals that do not provide 15 point types by default.
Another use is to set the point cycle equal to the line cycle, if you always want them to match.
This patch can be applied to either 5.0 or 5.1
