[Gptfdisk-general] Adding support for GPT recovery using sgdisk

[abhisek s. <abh...@gm...>]

Hi All,

The sgdisk utility currently lacks options for correcting the
Primary/Secondary GPT headers if there is any corruption  If the
Primary GPT header is corrupted, it could be updated from the
Secondary GPT header and vice-verse.

I have prepared a patch for this(PFA). Kindly review it and add it the sources.

Please do let me if there are additional changes required. This patch
has been prepared on the latest version of the code i.e.  0.8.10

Thanks,
Abhisek