IcuTimeZoneProvider: refer to UnicodeString with prefix 'icu::'
IcuTimeZoneProvider: refer to UnicodeString with prefix 'icu::'

[1] http://bugs.icu-project.org/trac/ticket/13460
[2] http://source.icu-project.org/repos/icu/trunk/icu4c/readme.html#RecBuild.

Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server