This is to work around the file permissions problems with the
standard System.Directory.copyFile function. When installing
files we do not want to copy permissions or attributes from the
source files. On unix we want to use specific permissions and
on windows we want to inherit default permissions. On unix:
copyOrdinaryFile   sets the permissions to -rw-r--r--
copyExecutableFile sets the permissions to -rwxr-xr-x