Make the testcase more stable and faster. Reduce code.
JIRA issue: CORE-13950
- Use WM_COPYDATA message to communicate with shell32_apitest_sub.exe.
- Use concept of "stage" and "step".
- Do multiple checks in one step.
- Flush notification by using (SHCNF_FLUSH | SHCNF_FLUSHNOWAIT) flags.