Link Manager is disabled even if you have custom links

[SergeyBiryukov]

When upgrading from 3.4.2, link manager is disabled even if you have links, due to inaccurate $wp_current_db_version check in upgrade_350().

We check for version 21501, however it was bumped to 21707 in [21710].

Related: ​http://wordpress.org/support/topic/links-50?replies=19#post-3433313.

[SergeyBiryukov]

22626.patch​ uses version 22006, which is 3.5-beta1.

[nacin]

Oh man. That's fun. I saw a few reports in the forums, but it worked for me in a brief test. Great catch.

[nacin]

Took me a few moments to fully understand the report. To be clear, we handled the links upgrade routine in r21501, but after that, we bumped the DB version for 3.4.2, to the current revision, 21707. Obviously, 21501 < 21707, so upgrades weren't firing when you went from 3.4.2 to trunk.

In the future, we should probably just increment by 1 in a branch. It's so rare and usually is only to flush rewrite rules.

[nacin]

In 22911:

Fix disabling of the link manager on upgrade from 3.4.2 when there are no links.

In the 3.4 branch we bumped the DB version past the version used for disabling links in trunk, preventing it from running. In the future, we must avoid increasing branch DB version bumps to HEAD.

props SergeyBiryukov.
fixes #22626.