Fix off-by-one error in deciding to exit length calculation

The foreach starting at line 271 shouldn't be entered unless it is known $this->buffer[$start] through $this->buffer[$end] is set, inclusive (this is the range in the frame that holds the payload length).

Previously, we tested if `$end > strlen($this->buffer)`. Consider the case when `$end == strlen($this->buffer)`: $this->buffer[$end] is not set (because indexes start at zero). We should therefore instead test for `$end >= strlen($this->buffer)`.

Potentially fixes #35
listen() fix

Fixes 
Warning: stream_socket_accept(): SSL_R_NO_SHARED_CIPHER: no suitable shared cipher could be used.  This could be because the server is missing an SSL certificate (local_cert context option) in .../lib/Wrench/Socket/ServerSocket.php on line 87
Merge pull request #57 from positronium/master

listen() fix
Rate limiter fixes suggested by @supipd

- Allows configuration of the rate limiter options through the
  BasicServer's options
- Fixes the lack of a CLIENT_DATA event!
Merge pull request #62 from varspool/rate-limiter-fixes

Rate limiter fixes suggested by @supipd
Merge pull request #63 from varspool/frame-length-off-by-one

Fix off-by-one error in deciding to exit length calculation