Don't build facet in summary if facet is not active

This sounds like a great idea, if all the tests we have still pass we can indeed make a big win here.

We would need to have profiling data to back this up before this goes in (no matter what the patch is), so we can show off the improvements we made. Doing this with a tool such as boom/ab should be sufficient.

Setting to needs review so the testbot can see if something breaks.

Without patch:

boom -c 1 -n 100 http://search.dev/search/content?keys=pecus\&f%5B0%5D=content_type%3Aarticle

Summary:
  Total:	137.7983 secs.
  Slowest:	1.4593 secs.
  Fastest:	1.2816 secs.
  Average:	1.3780 secs.
  Requests/sec:	0.7257

With patch:

boom -c 1 -n 100 http://search.dev/search/content?keys=pecus\&f%5B0%5D=content_type%3Aarticle

Summary:
  Total:	140.7741 secs.
  Slowest:	1.7616 secs.
  Fastest:	1.2541 secs.
  Average:	1.4077 secs.
  Requests/sec:	0.7104

So there is a small increase in requests/second but not enough to notice. We should see if blackfire or xhprof gives us a better result - otherwise it looks like this doesn't really help.

No, I only have ~20 nodes on my testsite. I'll try again tonight/tomorrow.

I now have a facet with ~50 items (generated terms)

Summary:
  Total:	165.0995 secs.
  Slowest:	4.0573 secs.
  Fastest:	1.5837 secs.
  Average:	1.6510 secs.
  Requests/sec:	0.6057

With patch:

Summary:
  Total:	139.8320 secs.
  Slowest:	1.5906 secs.
  Fastest:	1.3638 secs.
  Average:	1.3983 secs.
  Requests/sec:	0.7151

Yeah, this is an awesome improvement. Thanks so much!

Thx!