Set the active flag in the PMBR when we install bootcode on a GPT partitioned disk.  Some BIOS require this to be set before they will boot the device.
Set the active flag in the PMBR when we install bootcode on a GPT
partitioned disk.  Some BIOS require this to be set before they will
boot the device.

Approved by:	marcel
MFC after:	2 weeks

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