Improve R wrapper error message calling overloaded methods

when incorrect types passed are passed to the overloaded methods.

Old unhelpful error message:
  Error in f(...) : could not find function "f"

Example of new improved error message:
  Error in use_count(k) :
    cannot find overloaded function for use_count with argtypes (NULL)

Examples/test-suite/r/li_boost_shared_ptr_runme.R

@@ -570,7 +570,7 @@ testSuite <- function() {
     k = m$SmartMemberValue;
     if (!is.null(k))
       stop("expected null");
-    #testSuite_verifyCount(0, k); # this does not work for nulls
+    testSuite_verifyCount(0, k); # this does not work for nulls
 
     # plain by value
     bNotCatched = F