Windows install to custom location after building from source

["Martin v. Löwis"]

> First, it relies on config.py whose existence msi.py
> optionally ignores.

Feel free to create a patch for that.

>  File "<COMObject Msm.Merge2.1>", line 2, in OpenDatabase
> pywintypes.com_error: (-2147352567, 'Exception occurred.', (0, None,
> None, None, 0, -2147024786), None)

This is 0x8007006e; 0x6E, in turn, might be ERROR_OPEN_FAILED.
Did you pass the file name of the MSI file? If not, it computed
one, and may have done so incorrectly.

Regards,
Martin