winspool: comments for "GetPrinterDriverDirectory updated" please

[Detlef Riekenberg]

Hi.

I ask for comments before sending this as 2 or 3 patches.

- Correct 2 failing tests on win9x
- Add Documentation for GetPrinterDriverDirectoryW/A (c2man)

- Add Function "validate_envW" to validate the user-supplied
  Printing Environment (respect "Windows Version" - Setting)
- Change GetPrinterDriverDirectoryW to Report the correct NT-Path
  or the win9x-Path on top of "validate_envW"

- Fix 2 Bugs in GetPrinterDriverDirectoryA
  (invalid Result from "needed" and possible Read from 0x00000000)
- 2 Tests are now working in Wine

"validate_envW" will be used by more Functions later.
(WINSPOOL_OpenDriverReg as Example)