[legacy] disable incompatible flags in legacy mode
[legacy] ignore more incompatible flags
[legacy] allows some more ignored formats
bootstrap
when passed to Printf, %l%n%L should be interepreted as %u, not %d
a testsuite to measure format behavior changes and the effectiveness of legacy mode
Add support for ignored scan_get_counter formats (%_[nlNL])
bootstrap
add typer support for the new formats
bootstrap
testsuite Makefile: use 'ocaml -init /dev/null' to avoid interferences with ~/.ocamlinit
testsuite for %_[nNlL]
[minor] introduce type aliases for simple padding and precision types
bootstrap
[legacy] allow incompatible or unsupported numeric formatting flags
parse the ignore flag before all others

The legacy implementation doesn't support "%+_", "%-_" etc. which were
accepted by Benoît's patches. This creates a discrepancy (though not
a regression) that is not necessarily desirable (and in any case makes
fuzz-testing for difference return non-bugs). Long-term, I think that
we're good with the previous, simpler structure where "_" must always
be the first flag.
fix printing bug: (Printf.printf "% 04d" 3) => "00 3"
[legacy] accept and ignore '+' and '-' before precision integers
[legacy] some characters were not allowed in charsets
minor strengthening of the typing of %{...%} formats