stackbuilder - wizard: Don't add default text to the installation

Log Message:
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Don't add default text to the installation selection combo. It only gets shown on GTK, and is rejected as an option until it is explicitly selected from the list.

Modified Files:
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wizard:
IntroductionPage.cpp (r1.19 -> r1.20)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/stackbuilder/wizard/IntroductionPage.cpp.diff?r1=1.19&r2=1.20)