This commit removes the simple/test-event-emitter-memory-leak test for
being unreliable with the new garbage collector: the memory pressure
exerted by the test case is too low for the garbage collector to kick
in.  It can be made to work again by limiting the heap size with the
--max_old_space_size=x flag but that won't be very reliable across
platforms and architectures.

If the string is external then the length can be quickly retrieved. This
is especially faster for large strings that are being treated as UTF8.
Also, if the string is external then there's no need for a full
String::WriteUtf8 operation. A simple memcpy will do.

* Change calls to String::New() and String::NewSymbol() to their
  respective one-byte, two-byte and UTF-8 counterparts.

* Add a FIXED_ONE_BYTE_STRING macro that takes a string literal and
  turns it into a v8::Local<v8::String>.

* Add helper functions that make v8::String::NewFromOneByte() easier to
  work with. Said function expects a `const uint8_t*` but almost every
  call site deals with `const char*` or `const unsigned char*`. Helps
  us avoid doing reinterpret_casts all over the place.

* Code that handles file system paths keeps using UTF-8 for backwards
  compatibility reasons. At least now the use of UTF-8 is explicit.

* Remove v8::String::NewSymbol() entirely. Almost all call sites were
  effectively minor de-optimizations. If you create a string only once,
  there is no point in making it a symbol. If you are create the same
  string repeatedly, it should probably be cached in a persistent
  handle.

Commit 847c6d9 adds a 'project headers before system headers' check
to cpplint. Update the files in src/ to make the linter pass again.

Prior, strings would first be converted to a Buffer before being written
to disk. Now the intermediary step has been removed.

Other changes of note:

* Class member "must_free" was added to req_wrap so to track if the
  memory needs to be manually cleaned up after use.
* External String Resource support, so the memory will be used directly
  instead of copying out the data.
* Docs have been updated to reflect that if position is not a number
  then it will assume null. Previously it specified the argument must be
  null, but that was not how the code worked. An attempt was made to
  only support == null, but there were too many tests that assumed !=
  number would be enough.
* Docs update show some of the write/writeSync arguments are optional.

The method is useful elsewhere when needing to check if external and
grab data.

Conflicts:
	AUTHORS
	ChangeLog
	deps/uv/ChangeLog
	deps/uv/src/version.c
	deps/uv/src/win/fs.c
	src/node.cc
	src/node_crypto.cc
	src/node_os.cc
	src/node_version.h

Performs a quick, non-exhaustive check on the input string to see if
it's compatible with the specified string encoding.

Curently it only checks that hex strings have a length that is a
multiple of two.