icu4c api proposal: add operator + for UnicodeString

I propose to add an operator + for UnicodeString (unistr.h):

/**
  * Create a new UnicodeString with the concatenation of two others.
  *
  * @param s1 The first string to be copied to the new one.
  * @param s2 The second string to be copied to the new one, after s1.
  * @return UnicodeString(s1).append(s2)
  * @draft ICU 2.8
  */
inline UnicodeString
operator+ (const UnicodeString &s1, const UnicodeString &s2);


Our intltest suite has actually had this operator for a long time. This is essentially a move from 
the test suite to the public header.

I am not moving the overloads (string + integer etc.) from intltest.h because they are really just 
test suite helpers, and their functionality is much better served with NumberFormat and other 
classes. Also, unistr.h already suffers from overloaditis...

Expiration: Friday, 2003-nov-07

Sincerely,
markus