Write UNION() for MERGE tables

Docs/manual.texi:
  Clearify when logging is done
myisam/myisamchk.c:
  Better error message
mysql-test/r/merge.result:
  Added test for SHOW CREATE on MERGE table
scripts/safe_mysqld.sh:
  Search by default in database directory
sql/ha_myisammrg.h:
  Add UNION() to SHOW CREATE TABLE
sql/sql_update.cc:
  removed compiler warning

scripts/safe_mysqld.sh

@@ -72,6 +72,10 @@ then
   MY_BASEDIR_VERSION=$MY_PWD		# Where bin, share and data are
   ledir=$MY_BASEDIR_VERSION/bin		# Where mysqld is
   DATADIR=$MY_BASEDIR_VERSION/data
+  if test -z "defaults"
+  then
+    defaults="--defaults-extra-file=$MY_BASEDIR_VERSION/data/my.cnf"
+  fi
 # Check if this is a 'moved install directory'
 elif test -f ./var/mysql/db.frm -a -f ./share/mysql/english/errmsg.sys -a \
  -x ./libexec/mysqld