StarBrowser fails to install in a 3.7-5595 image with squeakmap 2
installed.  It's SBSqueakMap.st file includes a declaration for class
SMCard which no longer exists. Removing that declaration allows SB
to install (at what cost, I don't know).

Side issue: it would be nice if Package Loader (?) provided a way to get
from the simple installation error popup to a debugger (or just a more
verbose error message) to help debug these.