Fix mbind flags definition.

What we had in the 'flags' field should have been OR'd into the 'mode' field.
Move them to the right place, and then add the actual flags that should have
been in the flags field.
re-use testfile filename buffer instead of re-allocating it
remove old testfiles on startup if they exist
if testfile creation fails, retry instead of failing hard
if testfile creation is spinning without progress, output errno
fix mmap2 definition in ppc syscall table
remove pointless chmod

Any permissions problems will be on the directory, not the filename,
so modifying the perms of the file before we unlink it is pointless.