[imp] Enable tests for php 5 on travis
Closes #3898
[bug][33344] Wrong filename detection of Content-Disposition URL headers. Fixes #3182
[imp][33446] Moving the readmore button to layouts;
Closes #3702
Codestyle
[bug][33103] Import the user plugins for onUserLoginFailure.
Fixes #2761
[imp][32762] improve jquery selector
Closes #3902
[bug][33942] Consistent use of clearfix in com_installer.
Fixes #3887
Codestyle; Closes #3903
Merge branch 'staging' into 3.4-dev