stream: Properly handle large reads from push-streams

Problem 1: If stream.push() triggers a 'readable' event, and the user
calls `read(n)` with some n > the highWaterMark, then the push() will
return false (indicating that they should not push any more), but no
future 'readable' event is coming (because we're above the
highWaterMark).

Solution: return true from push() when needReadable is set.

Problem 2: A read(n) for n != 0, after the stream had encountered an
EOF, would not trigger the 'end' event if the EOF was pushed in
synchronously by the _read() function.

Solution: Check for ended in stream.read() and schedule an end event if
the length now equals 0.

Fix #4585
assert that require() has a truthy path
TypedArrays: Improve dataview perf without endian param

V8 seems to be particularly slow converting an undefined value to false
in BooleanValue.

Revert this when we upgrade to V8 3.17, or whenever the fix discussed
in http://code.google.com/p/v8/issues/detail?id=2487 lands in V8.
repl: fix how to module requiring in code comment

This module requiring style is old.
This API has been changed in Node 0.1.16 726865af.
lint: Prefer double-quotes over single
module: assert that require() is called with a string

as requested in #4577
test: add module-loading test with empty string