[Rd] Two small fixes for WRE

[Ivan Krylov]

There is one unintended use of \R instead of @R{}, and the prototype of
Rf_acopy_string needs a small fix:

Index: doc/manual/R-exts.texi
===================================================================
--- doc/manual/R-exts.texi	(revision 90457)
+++ doc/manual/R-exts.texi	(working copy)
@@ -15492,7 +15492,7 @@
 @c @apifun Free
 @c The R_ forms were introduced in 2016-09, hence for R 3.4.0
 Historically the macros @code{Calloc}, @code{Free} and @code{Realloc}
-were used but have been removed in \R 4.5.0.
+were used but have been removed in @R{} 4.5.0.
 
 @code{R_Calloc}, @code{R_Realloc}, and @code{R_Free} are currently
 implemented as macros expanding to calls to @code{R_chk_calloc},
@@ -17044,7 +17044,7 @@
 @end deftypefun
 
 @eapifun Rf_acopy_string
- using deftypefun {const char *} Rf_acopy_string (const char *@var{in})
+ using deftypefun {char *} Rf_acopy_string (const char *@var{in})
 Return a copy of a string using memory from @code{R_alloc}.
 @end deftypefun

 
-- 
Best regards,
Ivan