give markers a stacked option

[t6nnp6nn]

Referring to this discussion:

https://groups.google.com/forum/?fromgroups#!topic/flotr2/FsMZhZmgOT0%5B1-25%5D

using markers on a stacked chart (bar or line) currently is not usable (with bars/lines stacked and markers unstacked). The workaround referred in the discussion is usable but not very reasonable. A built in stacked markers options would be a logical option for stacked charts.

[cesutherland]

Here's an example: http://jsfiddle.net/davetarbox/U796V/3/