linestyle option for FancyArrowPatch and similar commands

Hi all,

   I was wondering why there are inconsistent values for the 'linestyle' option in matplotlib.backend_bases.GraphicsContextBase. The values allowed are 'solid', 'dashed', 'dotted' and 'dashdot', aside from tuples.

Compare this with the options available for the usual pyplot.plot() command, where the linestyles are '-', '--', '-.', ':', etc.

Is there a specific reason for the difference in the options? It doesn't seem too hard to add the options '-', '--', etc to the GraphicsContextBase class - one only needs to add these to a dict at