Restore a stub of the removed mysql_odbc_escape_string function
to fix a ABI breakage. The function was intended to be private
and used only by Connector/ODBC, but, unfortunately, it was exported
as part of the ABI. Nonetheless, only a stub is restored as the
original function is inherently broken and shouldn't be used.

This restoration only applies to MySQL 5.0. This will be addressed
differently in later versions -- reworked library versioning.

include/mysql.h:
  Restore mysql_odbc_escape_string prototype.
include/mysql_h.ic:
  Update ABI check.
libmysql/libmysql.c:
  Restore a mysql_odbc_escape_string stub.
libmysql/libmysql.def:
  Restore mysql_odbc_escape_string.
libmysqld/libmysqld.def:
  Restore mysql_odbc_escape_string.