v1.6.0

lotsa stuff
batch mode is slightly improved and now is the default keygen mode
configure stack size for new threads
fix intfilter expansion logic
adjust autoconf.ac for newer autoconf versions
passphrase checkpointing contributed by @scribblemaniac
rebase on newer SUPERCOP & use PIE mode when compiling
various other fixups & cleanups
changeset: v1.5.0...v1.6.0
also no minisign because my key is dead