support more character encoding in incoming emails (#15785)

Supporting encodings of iconv on Ruby 1.8 depend on iconv implementation.
glibc-common-2.12-1.132 on CentOS6 does not support ks_c_5601-1987.

Contributed by Felix Schäfer.

git-svn-id: http://svn.redmine.org/redmine/trunk@12474 e93f8b46-1217-0410-a6f0-8f06a7374b81
svn propset svn:eol-style native test fixture (#15785)


git-svn-id: http://svn.redmine.org/redmine/trunk@12475 e93f8b46-1217-0410-a6f0-8f06a7374b81