[Rd] class extension and documentation

[Terry Therneau]

I've added a "backsolve" method to the bdsmatrix library.
Per the Extending manual section 7.1 I've also added the following 3
lines along with my setMethod definitions for 2 classes.

backsolve <- function(r, ...) UseMethod("backsolve")
backsolve.default <- base:::backsolve
formals(backsolve.default) <- c(formals(backsolve.default), alist(...
= )) 

I've also added a backsolve-methods.Rd page, though since my arguments
are identical to the default it doesn't say much.  And, after a test
failed, added the new backsolve.default routine to my export list.

Now R CMD check claims that I need Rd pages for backsolve and
backsolve.default.  I don't think I should rewrite those.  
   How do I sidestep this  and/or
   what other manuals should I read?

Perhaps do setMethod("backsolve", signature(r="ALL"),
                           base:::backsolve(r, ...))
instead?

Terry Therneau