Integrate abartlet's t_push_ucs2 test into test framework:

Integrate abartlet's t_push_ucs2 test into test framework:

 - Build t_push_ucs2 as part of check-programs, the prerequisite for
   "make check".

 - t_push_ucs2.c: Load configuration from /dev/null so that we get a
   unix_charset of UTF-8 and can do meaningful UCS2 tests.  Better
   comment.

 - Add a test to strings.py which tries conversion UTF8->UCS2->UTF8
   and checks the results.  Do this for English, Latin-1, and Katakana
   strings.

 - Add Python module with symbolic names for a handful of UNICODE
   characters.