Improve documentation and make all the various axis calls more consistent with each other following Joao's recommendation.  I have also tested this code (and the logic change in c_plaxes in plbox.c) for all varieties of allowed axis values.
Improve documentation and make all the various axis calls more consistent
with each other following Joao's recommendation.  I have also tested this
code (and the logic change in c_plaxes in plbox.c) for all varieties of
allowed axis values.

svn path=/trunk/; revision=2706

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot