Redmine

This issue functions as a placeholder to make sure this change gets included on the changelog.

The (functionality of the) awesome_nested_set gem, that is used for building trees of projects and issues, is replaced with a simple and more robust custom implementation of nested sets. This fixes several dead locks and/or nested set inconsistencies.

This change is completed by Jean-Philippe Lang (I'll assign this issue accordingly) with the following related changesets: r13841, r13842, r13843, r13844, r13845 and r13846.