Porting glean to new environments

Thanks to Johan Smet, we have a working version of glean for Microsoft Windows, using Visual C++ version 6.

Porting glean to BeOS and MacOS would be well worthwhile.

Porting glean to other UNIX variants should be straightforward, but I haven't looked into it.

In all of these cases, most of the work is in the window system code (src/libs/dsurf, src/glean/winsys.cpp, src/glean/dsurf.cpp). Some other things are needed in src/libs/timer and src/glean/environ.cpp. It's always possible that differences in compilers will result in a need for more pervasive changes; some problems of this type did arise during the port to Windows.