MEDIUM: tools: improve time format error detection

MEDIUM: tools: improve time format error detection

As reported in GH issue #109 and in discourse issue
https://discourse.haproxy.org/t/haproxy-returns-408-or-504-error-when-timeout-client-value-is-every-25d
the time parser doesn't error on overflows nor underflows. This is a
recurring problem which additionally has the bad taste of taking a long
time before hitting the user.

This patch makes parse_time_err() return special error codes for overflows
and underflows, and adds the control in the call places to report suitable
errors depending on the requested unit. In practice, underflows are almost
never returned as the parsing function takes care of rounding values up,
so this might possibly happen on 64-bit overflows returning exactly zero
after rounding though. It is not really possible to cut the patch into
pieces as it changes the function's API, hence all callers.

Tests were run on about every relevant part (cookie maxlife/maxidle,
server inter, stats timeout, timeout*, cli's set timeout command,
tcp-request/response inspect-delay).