We also never really tested this, because we run make distcheck, which
does another configure with default flags instead of the ones we passed.
Fixes#317.
- This PR also adds a DEBUG cmake option that enables -DTOX_DEBUG.
- We also remove `-Wall`, because there are too many warnings, and nobody really
looks at them at the moment. We'll see about fixing them soon. We'll also want
to enable `-Werror` at some point.
- Finally, this PR enables `-O3` to make sure toxcore still works correctly
under heavy compiler optimisations.
If libsodium can't be found with PKG_CHECK_MODULES, try AC_CHECK_LIB. If that
also fails, abort configure. If a user passes --with-libsodium-libs explicitly,
that overrides the pkg-config found location.
Also, fix the hstox build that was taking half an hour. It now takes 5 minutes.
Also, perform distcheck on travis to ensure that make dist works. It's not
actually failing the build at the moment due to broken tests.
