[DateTime]: unexpected boost::local_time::bad_offset caught

Hi,

I stumbled over an inconsistency in the Boost::DateTime library. I 
wanted to create a STL map of posix time zones. For this purpose, I 
wrote a mini code generator:

----------------------------------------------------
tz_database tz_db;
tz_db.load_from_file("src/date_time_zonespec.csv");

vector<string> names = tz_db.region_list();

for (vector<string>::iterator it = names.begin();
      it != names.end(); ++it)
    cout << "   timeZones.insert(pair<string, time_zone_ptr>(\""
         << *it << "\", "
         << "time_zone_ptr(new posix_time_zone(\""
         << tz_db.time_zone_from_region(*it)->to_posix_string()
         << "\"))));"
         << endl;
----------------------------------------------------
(Sorry for the bad formatting)

This created lines like the following:

----------------------------------------------------
timeZones.insert(pair<string, time_zone_ptr>("America/New_York", 
time_zone_ptr(new 
posix_time_zone("EST-05EDT+01,M3.2.0/02:00,M11.1.0/02:00"))));
[...]