stackbuilder - wizard: Use a timer to update the download progress

Log Message:
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Use a timer to update the download progress dialogue, rather than doing it every N bytes. Also, display the download speed.

Modified Files:
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wizard:
App.cpp (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/stackbuilder/wizard/App.cpp.diff?r1=1.6&r2=1.7)
wizard/include:
App.h (r1.5 -> r1.6)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/stackbuilder/wizard/include/App.h.diff?r1=1.5&r2=1.6)