i3 - improved tiling WM

Disallow using reserved wspace namespace in config

Patch status: needinfo

Patch by Alexander Berntsen

To apply this patch, use:
curl http://cr.i3wm.org/patch/518/raw.patch | git am

b/src/workspace.c

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@@ -142,6 +142,10 @@ Con *create_workspace_on_output(Output *output, Con *content) {
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             continue;
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         if (*target == '"')
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             target++;
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+        if (strncasecmp(target, "__", strlen("__")) == 0) {
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+            LOG("You cannot switch to the i3 internal workspaces.\n");
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+            continue;
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+        }
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         FREE(ws->name);
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         ws->name = strdup(target);
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         if (ws->name[strlen(ws->name)-1] == '"')