Documentation wrong for precedence of 'Lx' and 'dx' for NonUniformGrids

[guyer]

The documentation for fp.Grid1D, etc., says "If Lx is specified the length of the domain is always Lx regardless of dx", but this is not true if dx is an explicit list of spacings. E.g.,

mesh = fipy.Grid2D(nx=5, dy=[1]*2+[.5]*4, Lx=3, Ly=1)

will produce a grid six elements high of total height 4. This is the "correct" result, but not what the documentation says will happen.

See http://stackoverflow.com/a/32704639/2019542.