ticket:10532 ICU Charset Detector, port UTF-16 enhancements from Java to C

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@34730 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10553: RelativeDateFormat copy constructor was incomplete

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@34731 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10557: Fix some zOS build errors caused by missing exports and pthread macros

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@34733 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10549: Fixed some problems in test case description in collperf2.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@34734 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10559 Fix C++ compilation errors with U_OVERRIDE_CXX_ALLOCATION=0

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@34736 251d0590-4201-4cf1-90de-194747b24ca1