Update devel/mtbl to version 1.2.1:
- Prevent fileset reloading when the fileset has iterators open.
- Add and document facility to disable reloading of filesets.
- Defer initial load of fileset until the first operation on a fileset source.
- Handle 32bit size_t overflows, failing with an assertion upon opening an mtbl_reader with an oversized data block.
- Fix for systems with 32-bit size_t.
- Add several unit tests for various libmtbl functions.
- Correct a library versioning error.
Sponsored by: Farsight Security, Inc.