1) Rename the old shell tool "mysql_upgrade", to avoid a name collision.
2) Improve the spec file, to explicitly use a temporary socket.


scripts/mysql_upgrade_shell.sh:
  Rename: scripts/mysql_upgrade.sh -> scripts/mysql_upgrade_shell.sh
scripts/Makefile.am:
  The old shell script "mysql_upgrade" must be renamed, 
  so that its name does not collide with the new binary.
support-files/mysql.spec.sh:
  The previous version was incomplete, as it did not cover the case
  where the DBA had configured a non-default socket file.
  Solve that by creating and explicitly providing a temporary directory
  for the socket just for the duration of "mysql_upgrade", which also
  can be better protected than the default socket.