Fix the underlying non-literal-null-conversion instead of suppressing

The warning. What it was warning about was two calls to "g_strdup(NULL);",
which is a really dumb way of saying "NULL".

configure.ac

@@ -1323,9 +1323,6 @@ AX_CHECK_COMPILE_FLAG([-Wno-deprecated-register],
     [AM_CXXFLAGS="${AM_CXXFLAGS} -Wno-unused -Wno-deprecated-register"],
     [AM_CXXFLAGS="${AM_CXXFLAGS} -Wno-unused"], [-Werror])
 AC_LANG([C])
-AX_CHECK_PREPROC_FLAG([-Wno-non-literal-null-conversion],
-    [AM_CPPFLAGS="${AM_CPPFLAGS} -Wno-non-literal-null-conversion"],
-    [], [-Werror])
 AC_MSG_CHECKING(what extra warning flags to pass to the C compiler)
 if test ${GCC}x = yesx
 then

src/gnome-utils/gnc-tree-view-split-reg.c

@@ -5306,7 +5306,7 @@ gtv_sr_type_cb (GtkEntry    *entry,
         {
             /* If it's not there (or the list is empty) use default_flag */
             g_free (result);
-            result  = g_strdup (TXN_TYPE_NONE);
+            result  = NULL;
         }
     }
     else

src/register/ledger-core/split-register-model.c

@@ -1074,7 +1074,7 @@ gnc_split_register_get_vnotes_entry (VirtualLocation virt_loc,
     trans = xaccSplitGetParent (split);
 
     if(trans == NULL)
-        return g_strdup('\0');
+        return NULL;
     else 
         return xaccTransGetVoidReason(trans);
 }