stackbuilder - wizard: When a file to be downloaded already exists but

Log Message:
-----------
When a file to be downloaded already exists but the checksum doesn't match, instead of changing the name we save to,
renamethe existing file (by appending .YYYYMMDDHHMMSS). We need to do this because renaming the msi maks Bad Things
Happenwhen we try to upgrade. 

Modified Files:
--------------
    wizard:
        App.cpp (r1.13 -> r1.14)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/stackbuilder/wizard/App.cpp.diff?r1=1.13&r2=1.14)
    wizard/include:
        App.h (r1.9 -> r1.10)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/stackbuilder/wizard/include/App.h.diff?r1=1.9&r2=1.10)