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.
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.
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.
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