Xpra: Ticket #560: restore the ability to run under wine

versions before 0.12 can be installed in wine and will run reasonably well. Good thing about wine is that we get meaningful backtraces right out of the box, unlike with the abysmal dr watson..

#495 broke this and the installation fails with:

fixme:process:SetProcessDEPPolicy (1): stub
fixme:process:SetProcessDEPPolicy (1): stub
fixme:win:DisableProcessWindowsGhosting : stub
fixme:wbemdisp:locator_ConnectServer 0x12d910, L"", L"root\\CIMV2", L"", 0x12d92c, L"", L"", 0x00000000, (nil), 0x33fa28

We should either:

• detect we are running under wine is running and skip the process check
• add an installer command line parameter to switch the test off