Separate search results for handbooks and P2/blog

[siobhan]

When I do a search on make/core, it displays pages from the handbook in the search results. So, for example, I [do a search for release leads](​http://make.wordpress.org/core/?s=%22release+lead%22) and the results display a page that I wrote in the handbook.

This feels out of place in these search results. The handbooks and the associated discussion blog should have separate searches.

[samuelsidler]

Agreed.

We should have two search boxes. I think we added handbook results because we only had one search box. Instead, let's have a search for the handbooks and a separate one for the the rest of the P2.

[coffee2code]

In 3234:

Handbook plugin: Add four template tags relating to handbook pages.

Specifically: wporg_get_handbook_post_types(), wporg_is_handbook(), wporg_is_handbook_post_type(), and wporg_get_current_handbook().

Props keesiemeijer.
See #515, #1671.
Fixes #1693.

[coffee2code]

In 3235:

Handbook plugin: Add template tag wporg_get_current_handbook_home_url() to get home URL for current handbook.

See #515, #1671.

[coffee2code]

In 3236:

Handbook plugin: Don't modify handbook archive query when handling search.

Allows for handbook-only searches.

See #515, #1671.

[coffee2code]

In 3237:

W.org P2 child theme: Add search.php template to handle loading handbook-specific template part (added as well) in search results.

See #515.

[coffee2code]

In 3238:

W.org P2 child theme: Add searchform.php template for context aware handbook/non-handbook search form submission URLs.

Fixes #515.