Proposal: add simpler case closure

Please respond by October 8.

Currently requesting case closure when getting the exemplar set for a 
locale (via ulocdata_getExemplarSet) will return a somewhat 
overenthusiastic case closure. For example, getting the exemplar set 
for en with the USET_CASE_INSENSITIVE option gives not [a-zA-Z] but 
[a-zA-Z\u017f\u212a]. This proposal is meant to address this issue.

Proposal:
1. Add a new constant, USET_SIMPLE_CASE_INSENSITIVE = 4 to uset.h.
2. Change UnicodeSet to pass this constant through to 
UnicodeSet::closeOver
3. Change closeOver to handle this option in addition to 
USET_CASE_INSENSITIVE.
4. If you specify both, it will ignore USET_SIMPLE_CASE_INSENSITIVE and 
do only USET_CASE_INSENSITIVE, because USET_CASE_INSENSITIVE is a 
proper superset of USET_SIMPLE_CASE_INSENSITIVE.

You can then pass USET_SIMPLE_CASE_INSENSITIVE to 
ulocdata_getExemplarSet to get the "intuitive" behavior.

Deborah