Final cleaning and stabilization

In this commit, I restored the files to their most up-to-date form. In
other words, I found some contamination from old code between the test
machine and the production machine (github is only in the production
one). I fixed this contamination. Html2faxcover is working perfectly. I
also introduced file locking in both html2faxcover and faxrecvd to
prevent any rare but possible races for using the tmp directory. I think
I fixed an issue in which missing commandline parameters or null
commandline parameters could seriously create undefined behavior with a
crash in most situations. Both programs clean the tmp directory before
and after operations to prevent leftovers if the programs crash.