More portable version of unpack_file


git-svn-id: https://fricas.svn.sourceforge.net/svnroot/fricas/trunk@1778 b0c55286-4f34-0410-a049-a1e7e93b0762
Make sure .spad files are correct Spad


git-svn-id: https://fricas.svn.sourceforge.net/svnroot/fricas/trunk@1779 b0c55286-4f34-0410-a049-a1e7e93b0762