context 7.x-3.0-beta4

#1451830 by tekante: Ensuring a clean error message instead of a PDO error message is generated when trying to create a context with a duplicate name
#1496236 by tekante: Upgrade from D6 to D7 broken - removed Drupal 6 hook_update_N functions from .install file
#1178008 by adamdicarlo: context_layout_theme() no-template PHP notice.
#1459620 by andrew_k, wbobeirne, tekante: Make exclude symbol clearer in condition description
#1251240 by dalin: Context block reaction lists blocks without calling hook_block_info_alter().
#606816 by milesw, nlisgo: Node forms drop out of context on validation error

Working towards a release candidate for 7.x, please see issues marked as D7 stable release blocker and comment on patches, debate whether they should be considered a blocker and lobby for items you feel are missing from the release blocker list.