[PATCH] atl: Fix the ATL_WNDCLASSINFOW::m_szAutoName member definition and construction.

[Hermès BÉLUSCA-MAÏTO]

- Document the m_szAutoName size.

- Make the format actually MS-compatible: "ATL" followed by colon,
  followed by hexadecimal digits of pointer (4*2 digits on 32-bit platforms,
  8*2 digits on 64-bit platforms). This correctly fix x64 compilation
  and still make the autogenerated name "unique".

- Add a test that checks the name prefix.

Signed-off-by: Hermes Belusca-Maito