ticket:10983 Add failure checks to utext_clone().

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@35986 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10976 Remove C++ null reference checks; they're undefined behavior.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@35987 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10908 LocaleDisplayNames thread safety fix.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@35989 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10903 u_strToUTF8WithSub(), API docs misleading regarding error status setting.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@35991 251d0590-4201-4cf1-90de-194747b24ca1