Undo change: https://github.com/chamilo/chamilo-lms/pull/346
Minor format code.
Show only visible exercises see BT#7237
Only active exercise see #7237
Show only visible exercises see BT#8699
Only active exercise see #7237
Minor - format code
Fixing session special page see BT#8700
Minor - removing whitespaces.
Fix PDF header date to use local time - refs BT#7286
Merge branch '1.9.x' of github.com:chamilo/chamilo-lms into 1.9.x
Fixing old links see BT#8704
Minor - format code.
Split social_left_content in blocks at tpl level - refs #5637
Minor - code style review - refs #5637
Merge branch '1.9.x' of github.com:chamilo/chamilo-lms into 1.9.x
Split social_left_content in blocks at tpl level in messaging tool - refs #5637
Fix typo in credits
Minor - format code.
Fixing some fatal error when the plugin is not activated

Tested with php 5.4.33-1