Truncated message box due to short fixed buffer size in ShellMessageBoxW

Truncated message box due to short fixed buffer size in ShellMessageBoxW (WCHAR[100] only while some text ressources are longer)

As discussed with hbelusca and learn_more good design would be :

• shell32!ShellMessageBoxW directly redirecting to the WrapW function from shlwapi,
• and, instead of keeping the current ShellMessageBoxA, its new implementation could just convert what's needed into unicode and call ShellMessageBoxW.