Drupal 7.23, 2013-08-07
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- Added a drupal_check_memory_limit() API function to allow the memory limit to
  be checked consistently (API addition).
- Added protection to cache_clear_all() to ensure that non-cache tables cannot
  be truncated (API addition: a new isValidBin() method has been added to the
  default database cache implementation).
- Added a drupal_array_diff_assoc_recursive() function to allow associative
  arrays to be compared recursively (API addition).

Drupal 7.22, 2013-04-03
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- Changed various field API functions to allow them to optionally act on a
  single field within an entity (API addition: http://drupal.org/node/1825844).
- Added an empty "datatype" attribute to taxonomy term and username links to
  make the RDFa markup upward compatible with RDFa 1.1 (minor markup addition).
- Refactored the Field module's caching behavior to obtain large improvements
  in memory usage for sites with many fields and instances (API addition:
  http://drupal.org/node/1915646).
- Added an assertThemeOutput() method to Simpletest to allow tests to check
  that themed output matches an expected HTML string (API addition).
- Added an optional "exclusive" flag to installation profile .info files which
  allows Drupal distributions to force a profile to be selected during
  installation (API addition: http://drupal.org/node/1961012).

Drupal 7.17, 2012-11-07
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- Added hook_entity_view_mode_alter() to allow modules to change entity view
  modes on display (API addition: http://drupal.org/node/1833086).

Drupal 7.15, 2012-08-01
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- Introduced a 'user_password_reset_timeout' variable to allow the 24-hour
  expiration for user password reset links to be adjusted (API addition).
- Changed the drupal_array_get_nested_value() function to return a reference
  (API addition).
- Fixed data loss issue due to field_has_data() returning inconsistent results.
  The fix adds an optional DANGEROUS_ACCESS_CHECK_OPT_OUT tag to entity field
  queries which field storage engines can respond to (API addition:
  http://drupal.org/node/1597378).