Use libelf to find the location of the settings struct
Give better hints to the compiler on this logic
Reading should use MAP_PRIVATE
Reduce duplicated logic
Give a hint that we are sequentially reading memory

At least on FreeBSD this lowered page faults from 92 to 84
Don't remove the main binary when making a copy
Update bdlib for AtomicFile
Don't try munmap(NULL)
Use bd::AtomicFile to avoid cross-device renaming from Tempfile

This also removes the need for making a copy of the file. The copy was
never setup be restored anyhow.
Write userfile with AtomicFile
Import libelf 0.8.13
Build bundled libelf and link statically if needed
Document libelf change
Add missing libelf.m4
Update bdlib for AtomicFile
Hookup bdlib using new autotools system
Hookup bdlib configure as a AC_CONFIG_SUBDIRS
Don't hide errors building symbols and be sure to pass in proper -std
Update bdlib for AtomicFile
Update to latest depcomp