18.104.22.168: Minor changes to SB-COVER, SB-MD5 tests for Win32
* Have SB-COVER use md5sums of filenames for URLs.
* Have the test of SB-MD5:MD5SUM-FILE take the md5sum of a fresh empty
file, rather /dev/null or NUL, so that the test is independent of
any other limitations in CL:OPEN on Windows.
Richard M Kreuter