Hatch linewidth for pdf and ps backends (#235). - #1200

This pull request fails (merged 2ab206f into a7aaa83).

@mdboom: I we are going to merge this, we would probably want to use this value for the linewidth of the agg hatching too. From a quick scan, it looks like the value is currently hard-coded in _backend_agg.cpp at approx line 1225: hatch_path_stroke.width(1.0);.

The change should be implemented for SVG, Cairo and Mac OS-X backends as well.

Also, it would be useful to add a hatch.linewidth entry to the matplotlibrc.template file.

@mdboom, @pelson: The hatch docs indicate "Hatching is supported in the PostScript, PDF, SVG and Agg backends only." If we want to locate more places it needs to be fixed that's cool, and we should probably change the hatch docs? I don't have a vested interest in pushing this patch through (I haven't used this feature for over a year, but it seemed like someone cared about it again, and questions seem to pop up). Any help along the way would be appreciated.

_backend_agg.cpp never touches the rcParams and only uses the artists' properties. If we want to fix this for Agg and the other backends that don't have access to rcParams, we'll need to add a parameter to the artists.

For most, the parameters are set_{linewidth,hatch,linestyle,...}. hatchlinewidth seems too verbose. Would hatchwidth be a better parameter? Then we can change the rcParam to hatch.hatchwidth.

This does, however, lead to the problem that some of the hatch patterns are globally defined for the backend (PS, PDF). Should we ignore the getters and setters for the artists and just force a _hatchwidth parameter into the artists?

This iceberg is getting awfully big under the water.

PR is a year old so I'm closing it. Please feel free to update and re-invigorate this PR and it can be re-opened.

Personally, I'm interested in expanding hatching functionality in the near future to be able to control linewidth and color. Depending on how it goes, I'd also be interested in implementing custom hatch bitmap support for the backends which can support such a thing. But that is the future - in the meantime, please feel free to bring this PR back up to scratch.

Cheers!