Merge 3.4->default: asyncio: Fix upstream issue 168: StreamReader.read(-1) from pipe may hang if data exceeds buffer limit.

asyncio: Fix upstream issue 168: StreamReader.read(-1) from pipe may hang if data exceeds buffer limit.

source directory.

consolidating and improving human-validated tests of Idle. Change other files
as needed to work with htest.  Running the module as __main__ runs all tests.

s/Unix/POSIX/.

more accurate and sounds less like a strange tale of yore.

a Security Considerations section as preferred by both the devguide
and documentation users who do not wish to go insane.

Consolidates the logic for nlargest() into a single function so that
decoration tuples (elem,order) or (key, order, elem) only need to
be formed when a new element is added to the heap.  Formerly, a tuple
was created for every element regardless of whether it was added to
the heap.

The change reduces the number of tuples created, the number of ordering
integers created, and total number of tuple comparisons.

The paragraph above already says, clearly and correctly, that
"However, being completely deterministic, it is not suitable for
all purposes, and is completely unsuitable for cryptographic purposes."

Also we should make any promises about SystemRandom or os.urandom()
being cryptographically secure (they may be, but be can't validate
that promise).  Further, those are actual random number generators
not psuedo-random number generators.