show markers based on distance along line, split sequence behaviour into tuple and list/array
tightened up type checking. added some error handling.
Added a pylab example for markevery
wrote additional markevery tests in test_axes.py
added baseline images for markevery test in test_axes.py
Merge branch 'slice-and-fancy-indexing-for-markevery' of https://github.com/rtrwalker/matplotlib into slice-and-fancy-indexing-for-markevery

Conflicts:
	lib/matplotlib/lines.py