Port category_breadcrumb to D6

Since I'm the author of category_breadcrumb initial code, and running it on my live site too, I feel both need and responsibility to push this tiny sub-module to D6 sooner or later. Unfortunately, my time-budget is really tight these days, making the time frame a bit unpredictable.

As soon, as I'll find the time to start tries on upgrading my site to 6.x (now that the core of Category is here), I'll look into this. Expected time-frame: Anything between 1 week and 3 months, I really don't know.

Feel free to help, still.

I finally got to this work, so the D6 port of category_breadcrumb is ready (I hope):

- The administrative page is moved to a tab on admin/content/category now, to avoid cluttering the top-level admin page. Previously I thought it didn't really belong under the 'content' section, but since the wrapper modules are also there, and since it's all tied to the category module anyway, I finally moved it to have everything in one place (just like Pathauto moved to a tab on URL aliases). (This is the only real change, everything else works just like the 5.x version did.)

- The administrative page is now split to 'category_breadcrumb.admin.inc' as D6 commonly does (although it doesn't really make a lot of difference for a module this small).

- Several strings are corrected/rephrased, hopefully being more clear now, plus a bit of help added.

- Otherwise it's just a straightforward D5->D6 port.

I tested quite everything, and being the author of this code myself, I dare say it's fine. (Still hesitant to set RTBC on my own patch, though ;D )

Attaching both a patch (against the files found in CVS, one file added), and a tarball. Both contain the same.

I forgot to update the category/container check to the new $behavior way. Going to re-roll tomorrow (I hope).

Patch updated. (This was actually the first I did for Category-D6, I only learned about $behavior later.)