Merge lp://staging/~jtv/launchpad/bug-711077 into lp://staging/launchpad

[r=jcsackett,sinzui][bug=711077] Optimize +code-index.

= Summary =

Some +code-index indexes were timing out.

There were several main culprits:
 * Code to figure out whether a branch is attached to bugs was too roundabout.
 * Following references between objects can be costly even from cache.
 * Authors' names and icons were retrieved one icon at a time.
 * Complex tooltips with last-revision author info were constructed in TAL.
 * Counting and querying merge proposals is complex, costly, and duplicative.
 * ValidPersonCache is now a view, and hard to cache.

== Proposed fix ==

I addressed most of the issues I found, just not the last two ones: branch merge proposals and ValidPersonCache. It might help if we could get rid of the ValidPersonCache view in the schema at some point.

Fixes:
 * A new getBranchesWithVisibleBugs queries exactly what's needed, no more.
 * Many references can be bypassed using foreign keys' numeric values.
 * A new fetchAuthorsForDisplay queries persons, along with their icon info.
 * A new link formatter renders RevisionAuthor links directly in python.

== Pre-implementation notes ==

Robert felt that GIL issues might be behind the problem, so I had a profile taken. I was unable to make much of the results though, and so focused on conventional optimization.

== Implementation details ==

Tests for getBranchesWithVisibleBugs are direct descendants of existing ones for getBugBranchesForBranches, which I gradually reworked since they weren't being used anywhere else. The new code passed the old tests, but in the end I broke them down into smaller units with more explicit test goals.

== Tests ==

I ran all non-Windmill code tests plus test_bugbranch, and have a full EC2 run underway, but for a quick peek at the most you can run:

{{{
./bin/test -vvc lp.bugs.tests.test_bugbranch -t getBranchesWithVisibleBugs
./bin/test -vvc lp.code.browser.tests.test_revisionauthor -t RevisionAuthorFormatter
./bin/test -vvc lp.code.model.tests.test_revision -t fetchAuthorsForDisplay
}}}

== Demo and Q/A ==

This is an optimization branch, so don't expect any changes in functionality. But have a look at: https://code.qastaging.launchpad.net/openobject-addons/+code-index

That page should render fast enough (once qastaging's cache is warmed up to a realistic level) and not break. In fact a cowboyed version of the branch is running on qastaging as I write this.

= Launchpad lint =

Checking for conflicts and issues in changed files.

Linting changed files:
  lib/lp/code/templates/branch-listing.pt
  lib/lp/bugs/tests/test_bugbranch.py
  lib/lp/code/interfaces/revision.py
  BRANCH.TODO
  lib/lp/app/browser/configure.zcml
  lib/lp/app/browser/tales.py
  lib/lp/bugs/interfaces/bugbranch.py
  lib/lp/code/model/tests/test_revision.py
  lib/lp/bugs/model/bugbranch.py
  lib/lp/code/model/revision.py
  lib/lp/code/browser/branchlisting.py
  lib/lp/code/browser/tests/test_revisionauthor.py