* 2.8: (22 commits)
Fix merge
[HttpFoundation] Use UPSERT for sessions stored in PgSql >= 9.5
[Console] fixed PHPDoc
[travis] HHVM 3.12 LTS
Fix feature detection for IE
[Form] Fixed collapsed choice attributes
[Console] added explanation of messages usage in a progress bar
force enabling the external XML entity loaders
[Yaml] properly count skipped comment lines
[WebProfilerBundle] Fix invalid CSS style
Added progressive jpeg to mime types guesser
[Yaml] Fix wrong line number when comments are inserted in the middle of a block.
Fixed singular of committee
Do not inject web debug toolbar on attachments
bumped Symfony version to 2.8.8
updated VERSION for 2.8.7
updated CHANGELOG for 2.8.7
bumped Symfony version to 2.7.15
updated VERSION for 2.7.14
update CONTRIBUTORS for 2.7.14
...
Conflicts:
CHANGELOG-2.7.md
CHANGELOG-3.0.md
src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
src/Symfony/Component/HttpKernel/Kernel.php
Fabien Potencier
Nicolas Grekas
Andrew Murray