devel/mtbl: Upgrade to version 1.5.0

• Add reader filter function option to mtbl_fileset.
• Use "galloping search" instead of full binary search for mtbl_iter_seek().
• Make index block verification optional for more efficient reader initialization.
• Fix underflow errors triggered by short keys and empty mtbl files.
• mtbl_fileset_partition() use is deprecated in favor of mtbl_fileset_dup() with the fname_filter_func option set.

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