Change skip plotting error bars to be unnoticeable.

[stuartcampbell]

The plotting in MantidPlot will intentionally skip drawing some error bars. For some data this is quite noticeable and means that the plots cannot be used for publications etc...

I think that we need to either alter the threshold of this plotting, and/or provide a means to disable it.

Or maybe, we should take the approach Origin has, which is to draw errors for all the points that are drawn, but for large data sets, only plot every N points.

[stuartcampbell]

This issue was originally trac ticket 1972

[stuartcampbell]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/1972/plot_spectra_problem.nx5
(uploaded by @stuartcampbell on 2010-12-02T21:53:04)

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