ctools 6.x-1.15

This is an incremental bugfix release for ctools, particularly for newer versions of php 5. (5.4+)

ctools is now in bug and security only maintenance mode. Any future feature requests should be made in the 7.x or preferably, the 8.x branch.

Changes since 6.x-1.14:

• #1334894 by mikeytown2: Warning: Invalid argument supplied for foreach() in views_content_views_content_type_render()
• #2599688 by jansete: Strict warning: Declaration of views_content_plugin_display_panel_pane::options_submit() should be compatible with views_plugin_display::options_submit(&$form, &$form_state)
• Fix 'Only variables should be passed by reference' error