"Renaming" means the icu namespace is suffixed with the version number,
atm icu_55. Using "renaming" allows to use two different versions of ICU,
thus easing upgrades. For instance haikuwebkit uses a current version of ICU,
while the system uses a newer one after an upgrade.
* Replace all uses of the icu namespace in our public headers, with a macro
defaulting to icu. As the namespace is only used for private fields pointers,
there should be no impact.
* Locale kit *.cpp have to import the macro from <unicode/uversion.h> *before*
including any locale headers. Ditto for a Time preferences cpp file. This way,
the correct current icu namespace is referenced.
* Fixes bug #12057.