Reading table with URL is doing many requests

If I read a web-based CSV file using `requests` it works straightaway and quickly:
```
In [62]: weather_url
Out[62]: 'http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1'

In [63]: dat = Table.read(requests.get(weather_url).text, format='ascii')
```
But if I do what I think is the equivalent directly with `Table.read` it's hitting the site many times and takes probably 10 times as long:
```
In [64]: dat = Table.read(weather_url, format='ascii')
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]
Downloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statenamDownloading http://www.wunderground.com/history/airport/KLAS/2010/3/1/CustomHistory.html?dayend=28&monthend=4&yearend=2010&req_city=NA&req_state=NA&req_statename=NA&format=1 [Done]

In [65]: 
```