slideshow/balloon: add `balloon-enable-3d'
doc repair
Fix `configure' for OpenBSD

"-rdynamic" doesn't work with GCC 4.7 on OpenBSD: "cc: error:
unrecognized command line option '-rdynamic'". The switch isn't
necessary because it is only a wrapper to "-Wl,--export-dynamic".
Look GCC bug 37454.
add 'so-mode to `system-type'

To work better with OpenBSD (which has been a problem since we
changed `ffi-lib' to open libraries in "local" mode by default).
openssl: remove special handling of OpenBSD

This special handling is now built into `ffi-lib'.
doc correction and test additions for `atan'

Closes PR 10324