Richard B's patch to enable users to explicitly request shadow bold

by disabling bold-font-name guessing (if their bold fonts are ugly).
I've turned the UI inside out, but the meat is pretty much the same.

[originally from svn r3410]

putty.h

@@ -470,6 +470,7 @@ struct config_tag {
     int stamp_utmp;
     int login_shell;
     int scrollbar_on_left;
+    int shadowbold;
     FontSpec boldfont;
     FontSpec widefont;
     FontSpec wideboldfont;