2.5-stable: pdf: fix failure exporting issue pdf with UTF-8 U+FFFD (#17826)

This revision has trunk r13368 and r13369 test.

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13370 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merged r13334 (#17486).

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13389 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merged r13390 (#17163).

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13397 e93f8b46-1217-0410-a6f0-8f06a7374b81
Merged r13404 from trunk to 2.5-stable (#17581)

stricter check of uploading attachments.

Contributed by fred bregar.

git-svn-id: http://svn.redmine.org/redmine/branches/2.5-stable@13405 e93f8b46-1217-0410-a6f0-8f06a7374b81
upgrade Ruby 2.1.3 and latest gems