std.net.curl: Bad timeout defaults

[Johannes Pfau]

I've been using std.net.curl lately and there's a small issue with the
default timeouts:

dataTimeout is documented as:
/// Set timeout for activity on connection.

but this is not true! timeout_ms actually is "the maximum time that you
allow the libcurl transfer operation to take". This timeout is enforced
even if there is activity. So we currently limit all CURL operations to
2 Minutes (default limit), which sucks for download managers and other
long-running operations.

We should probably use CURLOPT_LOW_SPEED_LIMIT and
CURLOPT_LOW_SPEED_TIME instead. Any comments?