Lots of changes to RichardsBorehole, and minor changes to the tests.  Th...

...is addresses issue #2750 .  Changes include: character is a function; well_constant added to user interface; auxvars added so RichardMaterial values do not need to be used; better algorithm for eigenvalues/vectors ; contribution behind and ahead-of is now better for boreholes with lots of points; and fixing some tabs and banned keywords