Fix issue with picture mode

- Fix issue with multiprocessing launching new UI instances
- Picture mode would not work as a result of this
- Roll target back to macos 10.12

cocoa/main.m

@@ -24,9 +24,17 @@ int main(int argc, char *argv[])
     Py_SetPythonHome(wPythonPath);
     Py_Initialize();
     PyGILState_STATE gilState = PyGILState_Ensure();
-    FILE* fp = fopen([mainpy UTF8String], "r");
-    PyRun_SimpleFile(fp, [mainpy UTF8String]);
-    fclose(fp);
+    /* This main gets called when multiprocessing spawns new threads.  To
+       prevent this from opening more windows and not working correctly we
+       are just checking main here and not running the file.  Should be able
+       to block on the python side of things but checking
+       __name__ == "__main__" did not seem to work in the one location I tried.
+     */
+    if ([NSThread isMainThread]) {
+        FILE* fp = fopen([mainpy UTF8String], "r");
+        PyRun_SimpleFile(fp, [mainpy UTF8String]);
+        fclose(fp);
+    }
     PyGILState_Release(gilState);
     if (gilState == PyGILState_LOCKED) {
         PyThreadState_Swap(NULL);