Rewrite console font changing.

 * Remove the old "Vista" code path in favor of two code paths:
    - setSmallFontVista: sets a TrueType font to match the code page
    - setSmallFontXP: uses SetConsoleFont to activate the smallest
      viable font in the console's font table

 * Selecting a CJK-specific TrueType font is important so that double-width
   characters occupy two cells in the console, which is important for
   maintaining consistency between the console and the Unix terminal.
   (Perfect consistency here might be impossible, but using the appropriate
   font improves things.)  winpty currently duplicates double-width
   characters, but that will be fixed soon.

agent/Agent.cc

@@ -24,6 +24,7 @@
 #include "Terminal.h"
 #include "NamedPipe.h"
 #include "AgentAssert.h"
+#include "ConsoleFont.h"
 #include "../shared/DebugClient.h"
 #include "../shared/AgentMsg.h"
 #include "../shared/Buffer.h"
@@ -82,7 +83,7 @@ Agent::Agent(LPCWSTR controlPipeName,
     m_bufferData.resize(BUFFER_LINE_COUNT);
 
     m_console = new Win32Console;
-    m_console->setSmallFont();
+    setSmallFont(m_console->conout());
     m_console->moveWindow(SmallRect(0, 0, 1, 1));
     m_console->resizeBuffer(Coord(initialCols, BUFFER_LINE_COUNT));
     m_console->moveWindow(SmallRect(0, 0, initialCols, initialRows));