Fixed bug in UNION


client/mysqlbinlog.cc:
  Added error message handling to read_log_event()
heap/hp_write.c:
  More debug info
myisam/myisampack.c:
  Cleanup
mysql-test/mysql-test-run.sh:
  Portability fixes.
mysql-test/r/union.result:
  More tests cases for UNION
mysql-test/t/union.test:
  More tests cases for UNION
sql/Makefile.am:
  Added mysql_embed.h
sql/item.cc:
  Fixed bug when using the same table multiple times in union.
sql/log_event.cc:
  Removed use of ## construct (Portability problem)
sql/log_event.h:
  Added error message handling to read_log_event()
sql/mysql_priv.h:
  Added mysql_embed.h
sql/opt_sum.cc:
  Cleanup
sql/slave.cc:
  cleanup
sql/sql_base.cc:
  Integrated table->ref_primary_key into table->part_of_key
sql/sql_union.cc:
  Cleanup
sql/table.cc:
  Integrated table->ref_primary_key into table->part_of_key
sql/table.h:
  Integrated table->ref_primary_key into table->part_of_key