bucket: correct broken unaligned load/store in armv5

armv5 devices and older (i.e. <= arm9 generation) require addresses that are
stored to and loaded from to to be 4-byte aligned.

If this is not the case the lower 2 bits of the address are cleared and the load
is performed in an unexpected order, including up to 3 bytes of data located
prior to the address.

Inlined buckets are stored after their key in a page and since there is no
guarantee that the key will be of a length that is a multiple of 4, it is
possible for unaligned load/stores to occur when they are cast back to bucket
and page pointer types.

The fix adds a new field to track whether the current architecture exhibits this
issue, sets it on module load for ARM architectures, and then on bucket open, if
this field is set and the address is unaligned, a byte-by-byte copy of the
inlined bucket is performed.

Ref: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15414.html

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