2. Slice of fix for Bug#42003 tests missing the disconnect of connections <> default

- If missing: add "disconnect <session>"
   - If physical disconnect of non "default" sessions is not finished
     at test end: add routine which waits till this happened
+ additional improvements
  - remove superfluous files created by the test
  - replace error numbers by error names
  - remove trailing spaces, replace tabs by spaces
  - unify writing of bugs within comments
  - correct comments
  - minor changes of formatting
Fixed tests:
  backup
  check
  compress
  grant
  information_schema
  multi_update
  overflow
  packet
  query_cache_not_embedded
  sp-threads
  subselect
  synchronization
  timezone_grant

mysql-test/t/synchronization.test

@@ -1,10 +1,13 @@
+# Save the initial number of concurrent sessions
+--source include/count_sessions.inc
+
 #
-# Test for Bug #2385 CREATE TABLE LIKE lacks locking on source and destination
-# table
+# Test for Bug#2385 CREATE TABLE LIKE lacks locking on source and destination
+#                   table
 #
 
 --disable_warnings
-drop table if exists t1;
+DROP TABLE IF EXISTS t1,t2;
 --enable_warnings
 
 connect (con1,localhost,root,,);
@@ -12,12 +15,12 @@ connect (con2,localhost,root,,);
 
 # locking of source:
 
-CREATE TABLE t1 (x1 int);
+CREATE TABLE t1 (x1 INT);
 let $1= 10;
 while ($1)
 {
   connection con1;
-    send ALTER TABLE t1 CHANGE x1 x2 int;
+    send ALTER TABLE t1 CHANGE x1 x2 INT;
   connection con2;
     CREATE TABLE t2 LIKE t1;
     replace_result x1 xx x2 xx;
@@ -25,7 +28,7 @@ while ($1)
     DROP TABLE t2;
   connection con1;
     reap;
-    send ALTER TABLE t1 CHANGE x2 x1 int;
+    send ALTER TABLE t1 CHANGE x2 x1 INT;
   connection con2;
     CREATE TABLE t2 LIKE t1;
     replace_result x1 xx x2 xx;
@@ -37,4 +40,11 @@ while ($1)
 }
 DROP TABLE t1;
 
+connection default;
+disconnect con1;
+disconnect con2;
+
 # End of 4.1 tests
+
+# Wait till we reached the initial number of concurrent sessions
+--source include/wait_until_count_sessions.inc