equality: struct transparency and inspector shortcuts and caching

Same as for hashing.
fix missing initialization of cached inspector reference

The 3m transformation fills it in, but it's obviously
better to be explicit and avoid the bug for CGC.
Some tweaks for Guide section 4
Improve Guide section 5
Guide chapter 6 tweaks
Use the `not-on-the-web' style *around* the installation comment.

Otherwise making it have a "display: none" style leaves a visible empty
div.
add macports default path as a place to look for aspell
Add contracts to net/dns functions.
Fix net/dns contracts
Improve Guide chapter 7

 * Typos/grammar
 * Fix breakdown of contract error message
 * Show `struct/dc` instead of deprecated lazy contracts
Fix broken link
Another small contract fix
Add DNS tests
Minor fix in Guide chapter 11
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