check whether greaseweazle.ino supports --fake-index, implement if not

[jepler]

greaseweazle host software has a --fake-index parameter. In this mode, the revolution is assumed to be of a certain duration, and no index is required by the capturing device (it might still be required by a PC-style drive in order to enable its flux output, but that's not true of a drive like disk ][ which never had any kind of index sensor).

check whether our gw-compatible firmware works in this mode and implement it if not.