[PATCH] Fixes some inconsistent partition types

We encountered a partition type 0x1C which wasn't known by Jnode.

Turns out 0x1B, 0x1C and 0x1E are supposed to correspond to 0x0B, 0x0C and 0x0E, except that the partitions are "hidden".

This patch adds in the missing one and also changes the naming to make these three consistent with the three further up the file.

(More after the break.)

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There is a further issue related to this, which is changing the behaviour when the partition type isn't one of the known ones -- any value could show up in reality and an unknown value is never a reason to throw an exception. Problem is that this is an enum, so I can't change it to return an unknown value unless we fill in bogus unknown values for every missing slot...

Also, in some situations it appears that multiple operating systems reserved the same partition number.

Just goes to show that there is merit to my other patches which avoid using this field to determine what filesystem is on the image.