Merged r11762 and r11763 from trunk (#13783).
Fix handling multiple text parts in email (#13646).
Patch by Alex Shulgin.
Issue#children is never nil (#14015).
Check inclusion only once (#14015).
Replaces camelcase variable names (#14015).
Removes some empty lines (#14015).
Removes then's (#14015).
Improved Issue#all_dependent_issues (#14015).
Patch by Jost Baron.
Improve plugins' Gemfile loading (#14028).