Add a GBU keyword per each level 1 extension

[mgalloy]

Allow some GBU tests to indicate which extensions failed the test, if appropriate.

Tasks

• make sure all the quantities that the GBU scheme will use are in the headers (primary and/or extension depending on the test)
• make sure the GBU tests only use these previously calculated values and the GBU thresholds, except for the sigma test
• write a utility routine to logical-and the GBU value in a header with a given value
• find a way to pass the GBU mask value for a given GBU test to it, or maybe a GBU test passes an array of failing extensions out and the caller handles setting the GBU value in the extension headers?
• adjust each GBU test to also record which extensions fail its condition, if appropriate
• checkout FXPOSIT to update header without completely re-writing file