parse-options.h: move PARSE_OPT_SHELL_EVAL between enums

Fix a bad landmine of a bug which has been with us ever since PARSE_OPT_SHELL_EVAL was added in 47e9cd28f8a (parseopt: wrap rev-parse --parseopt usage for eval consumption, 2010-06-12). It's an argument to parse_options() and should therefore be in "enum parse_opt_flags", but it was added to the per-option "enum parse_opt_option_flags" by mistake. Therefore as soon as we'd have an enum member in the former that reached its value of "1 << 8" we'd run into a seemingly bizarre bug where that new option would turn on the unrelated PARSE_OPT_SHELL_EVAL in "git rev-parse --parseopt" by proxy. I manually checked that no other enum members suffered from such overlap, by setting the values to non-overlapping values, and making the relevant codepaths BUG() out if the given value was above/below the expected (excluding flags=0 in the case of "enum parse_opt_flags"). Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>