Update software included under src/extra:
- tre
- trio:
only used on Windows.
- tzone: this
amounts to picking up the latest tzdata file, and on a
machine with a fully 64-bit zic (usually Linux, not OS X)
following the procedure in src/extra/tzone/Notes.
- win_iconv:
only used on Windows.
We don't update intl (originally for licence reasons, but
it reverted to LGPL 2.1).