various refinements to network implementation

The main idea is to make DatagramChannel and *SocketChannel behave in
a way that more closely matches the standard, e.g. allow binding
sockets to addresses without necessarily listening on those addresses
and accept null addresses where appropriate.  It also avoids multiple
redundant DNS lookups.

This commit also implements CharBuffer and BindException, and adds the
Readable interface.
implement Unsafe.{get|put}*Volatile
Merge pull request #213 from dicej/unsafe

implement Unsafe.{get|put}*Volatile
use x86_64-w64-mingw32- prefix for tools like dlltool as necessary

This fixes architecture mismatches when cross-compiling.
Merge pull request #214 from dicej/prefix

use x86_64-w64-mingw32- prefix for tools like dlltool
Merge pull request #212 from dicej/net

various refinements to network implementation
clean up System.getProperties and related methods

The behavior of Avian's versions of these methods was egregiously
non-standard, and there were problems with the Android implementations
as well.
Merge pull request #218 from dicej/properties

clean up System.getProperties and related methods
fix Java 6 build

Java 6's javac is not as smart as Java 7's when it comes to calling
overloaded methods from an inner class, so we have to be more
explicit.
Merge pull request #219 from dicej/java6

fix Java 6 build
fix some Unsafe bugs

 * Unsafe.arrayIndexScale was always returning the native word size,
   due to a thinko on my part

 * Unsafe.getLongVolatile and putLongVolatile did not work for array
   elements on 32-bit systems
Merge pull request #217 from bigfatbrowncat/avian-pack

Some improvements for Android lib core support
Update GH_TOKEN for Travis CI
Merge pull request #220 from dicej/unsafe

fix some Unsafe bugs
disable LTO by default

The -flto flag slows down linking dramatically without providing a
noticeable improvement in speed or size.  Rather than take the
build-time hit every time we rebuild, let's only do it when it's
explicitly requested.
Merge pull request #221 from dicej/lto

disable LTO by default
Update GH_TOKEN correctly this time.