delete remote source files that fail the md5 checksum test

Currently, if the build server downloads a file that fails the md5sum check
for some reason (perhaps interrupted download, etc), the file is never deleted
so the build can not succeed until someone manually deletes the bad file.  This
change deletes any file that is a remote source file / package that fails the
md5sum check.  The subsequent rebuild will then be forced to download the file
again.