Don't use strdup (non portable)

Author: asottile

src/context.cpp

@@ -133,7 +133,7 @@ namespace Sass {
 
   Context::~Context()
   {
-    // resources were allocated by strdup or malloc
+    // resources were allocated by malloc
     for (size_t i = 0; i < resources.size(); ++i) {
       free(resources[i].contents);
       free(resources[i].srcmap);

src/sass_functions.cpp

@@ -18,7 +18,7 @@ extern "C" {
   {
     Sass_Function_Entry cb = (Sass_Function_Entry) calloc(1, sizeof(Sass_Function));
     if (cb == 0) return 0;
-    cb->signature = strdup(signature);
+    cb->signature = sass_copy_c_string(signature);
     cb->function = function;
     cb->cookie = cookie;
     return cb;