Dodge some more potential protection issues

Author: kevinushey

inst/include/Rcpp/Environment.h

@@ -321,7 +321,8 @@ namespace Rcpp{
             Armor<SEXP> env ;
             try{
                 SEXP getNamespaceSym = Rf_install("getNamespace");
-                env = Rcpp_eval( Rf_lang2(getNamespaceSym, Rf_mkString(package.c_str()) ) ) ;
+                Shield<SEXP> package_str( Rf_mkString(package.c_str()) );
+                env = Rcpp_eval( Rf_lang2(getNamespaceSym, package_str) ) ;
             } catch( ... ){
                 throw no_such_namespace( package  ) ; 
             }

src/barrier.cpp

@@ -93,7 +93,8 @@ SEXP get_rcpp_cache() {
     if( ! Rcpp_cache_know ){
 
         SEXP getNamespaceSym = Rf_install("getNamespace"); // cannot be gc()'ed  once in symbol table
-        Rcpp::Shield<SEXP> RCPP( Rf_eval(Rf_lang2( getNamespaceSym, Rf_mkString("Rcpp") ), R_GlobalEnv) ) ;
+        Rcpp::Shield<SEXP> RcppString( Rf_mkString("Rcpp") );
+        Rcpp::Shield<SEXP> RCPP( Rf_eval(Rf_lang2( getNamespaceSym, RcppString ), R_GlobalEnv) ) ;
 
         Rcpp_cache = Rf_findVarInFrame( RCPP, Rf_install(".rcpp_cache") ) ;
         Rcpp_cache_know = true ;