[Rd] R_CHECK_FUNCS

[Patrick Welche]

I was compiling R on a system which admittedly was in the odd situation
that it declared a function in math.h, but didn't have the associated
implementation in libm, and the R 2.15.1 compilation failed.

It turns out that R_CHECK_FUNCS is rather less robust than the standard
AC_CHECK_FUNCS which actually attempts to link. On my temporarily broken
system, AC_CHECK_FUNCS would not have been fooled, and R would have
compiled successfully.

Thoughts on making R_CHECK_FUNCS simply an alias for AC_CHECK_FUNCS?

Cheers,

Patrick