This is terrible, but the OpenGL standard says that lines are half open, which means that one endpoint is not covered so adjoining lines don't overlap.  It also doesn't define which end is open, and indeed Mac OS X and Linux differ.  Mac OS X seems to leave the second endpoint open, but Linux uses the right-most endpoint for x major lines and the bottom-most endpoint for y major lines.

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extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404214