By default it looks like rake-compiler doesn't modify the gem spec
appropriately when we're cross-compiling for multiple Ruby versions.
Added some lines to remove "lib/fox16.so" from the gem spec's list
of files to include, and then added "lib/1.8/fox16.so" and "lib/1.9/fox16.so"
back to the list, so that we get the correct result.

Followed the instructions at http://github.com/luislavena/rake-compiler
to modify the ExtensionTask so that it supports cross-compilation. This
included moving the 'config_options' that were being used for a
RUBY_PLATFORM of "mingw" into the new 'cross_config_options' parameter.

In the interest of keeping this as simple as possible, I've extracted
the source files for the FXRuby User's Guide into a separate project
(fxruby-guide).

Modified the config_options for the ExtensionTask to point to the full DOS path for FOX installation