fix many LineReceiver slowdowns and bugs

New submission from ivank <[email protected]>:

LineReceiver can be slowed down by various input in three different ways.

The attached implementation:

        does not rely on string concatenation optimizations available in
        CPython 2.5+ and other implementations.

        stays fast when `data' contains many lines delivered at once, unless
        there is excess toggling between line mode and raw mode, with a large
        `extra' being passed to setLineMode each time.
            (note: many lines at once will be slow if Python is missing
            collections.dequeue, available since CPython 2.4)

        searches for the delimiter only in recently-received data, preventing
        unnecessary searching of the delimiter in a long buffer.

The attached implementation also fixes #3277 and #3050 and probably fixes #3353 because it no longer erroneously rejects lines under the MAX_LENGTH.

A related ticket is #2611 which is focused on fixing O(N**2) behavior in all protocols in protocols.basic

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Type     : defect
Component: core
Keywords : 
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/3803