Update net-im/spectral to latest upstream release.

After this afternoon's accidental update, fix the port and complete
the update.

• Spectral expects some unreleased and unpackaged dependencies, which is why the DISTFILES are a mess: it's gitlab, except this one dependency on github, and this other one.
• libQuotient is net-im/libQuaternion, except that spectral needs a newer-than-the-latest-unreleased version.
• there is a rather arbitrary and hackish patch to avoid a compile error -- during template expansion of visit() I sometimes got a compiler crash, more often an error about returning a value in a void function. Since the whole package is glued together with unreleased submodules, I spent some time trying to fix it, and then decided that this is non-essential functionality. Two events trigger the compile error, so I commented them out.

PORTREVISION bumped because there's a tiny chance that something
might have built out of the mess that there was earlier.