Handle out-of-range values in tor_parse_* integer functions

Handle out-of-range values in tor_parse_* integer functions

The underlying strtoX functions handle overflow by saturating and
setting errno to ERANGE.  If the min/max arguments to the
tor_parse_* functions are equal to the minimum/maximum of the
underlying type, then with the old approach, we wouldn't treat a
too-large value as genuinely broken.

Found this while looking at bug 5786; bugfix on 19da1f36 (in Tor
0.0.9), which introduced these functions.