curl.after_send hook: pass the $handle as parameter

[jrfnl]

Fixes #220

[jrfnl]

Before we actually action this, we should have a good look at the security implications of allowing access to the $handle (not just here).

[schlessera]

The curl.before_send already provides access to the $handle, so it is questionable in the end whether this would have any security implications that aren't already present anyway.

So we need to consider the following:

• What would be an extra issue with the "after send" access that wouldn't already be problematic with the "before send"?
• Is the "before send" already problematic enough that we need to act on it?