grid_graph dimensions and dim length

[Sergey Mitsyn <svm at jinr.ru>]

Hello,

I see that the documentation for grid_graph at http://www.boost.org/doc/libs/1_49_0/libs/graph/doc/grid_graph.html says that the number of dimensions should be greater than 2, but I can't really see why is that important while looking at the source code, and the test passes even for 1 dimension.

But it is clear that a dimension length must be greater than 2 if the dimension is wrapped, as in the opposite case (length=2) it is impossible to distinguish between wrapping and non-wrapping edge.

Maybe the documentation being intended to specify the lower limit for a dimension length rather than a dimensionality and requires a fix?

[Jeremiah Willcock]

(In [80642]) Removed incorrect note about restrictions on graph dimensionality and fixed other typos; fixes #6950