Log Message:
Changes 51.2:
Bug fixes:
* fix for enumset.h not being installed on Windows
* zOS pkgdata fix
* Test fixes
* Region enumeration fix
* make stable sort faster
* host failures for DateFormatTest
* LayoutEngine security patches (see above)
* ubrk fix for word_POSIX infinite loop
* fix memory leak/crash in LayoutEngine
* fix header guard typo in layout/TibetanReordering.h