merge some docs changes and a test case; null merge the code.

(we don't need to port the actual code from 5.1;
5.5+ do the relevant things differently, but correctly. the
test obviously is so it stays that way.)

mysql-test/r/variables.result:
  add test case.
mysql-test/t/variables.test:
  add test case.
strings/CHARSET_INFO.txt:
  clarify documentation

mysql-test/r/variables.result

@@ -1511,6 +1511,39 @@ SELECT @@skip_name_resolve;
 SHOW VARIABLES LIKE 'skip_name_resolve';
 Variable_name	Value
 skip_name_resolve	OFF
+#
+# Bug #43233 : Some server variables are clipped during "update,"
+#              not "check" stage
+#
+SET @kbs=@@global.key_buffer_size;
+SET @kcbs=@@global.key_cache_block_size;
+throw errors in STRICT mode
+SET SQL_MODE=STRICT_ALL_TABLES;
+SET @@global.max_binlog_cache_size=-1;
+ERROR 42000: Variable 'max_binlog_cache_size' can't be set to the value of '-1'
+SET @@global.max_join_size=0;
+ERROR 42000: Variable 'max_join_size' can't be set to the value of '0'
+SET @@global.key_buffer_size=0;
+ERROR HY000: Cannot drop default keycache
+SET @@global.key_cache_block_size=0;
+ERROR 42000: Variable 'key_cache_block_size' can't be set to the value of '0'
+throw warnings in default mode
+SET SQL_MODE=DEFAULT;
+SET @@global.max_binlog_cache_size=-1;
+Warnings:
+Warning	1292	Truncated incorrect max_binlog_cache_size value: '-1'
+SET @@global.max_join_size=0;
+Warnings:
+Warning	1292	Truncated incorrect max_join_size value: '0'
+SET @@global.key_buffer_size=0;
+ERROR HY000: Cannot drop default keycache
+SET @@global.key_cache_block_size=0;
+Warnings:
+Warning	1292	Truncated incorrect key_cache_block_size value: '0'
+SET @@global.max_binlog_cache_size=DEFAULT;
+SET @@global.max_join_size=DEFAULT;
+SET @@global.key_buffer_size=@kbs;
+SET @@global.key_cache_block_size=@kcbs;
 End of 5.1 tests
 
 #

mysql-test/t/variables.test

@@ -1243,6 +1243,50 @@ SET GLOBAL max_binlog_cache_size = @old_max_binlog_cache_size;
 SELECT @@skip_name_resolve;
 SHOW VARIABLES LIKE 'skip_name_resolve';
 
+--echo #
+--echo # Bug #43233 : Some server variables are clipped during "update,"
+--echo #              not "check" stage
+--echo #
+
+SET @kbs=@@global.key_buffer_size;
+SET @kcbs=@@global.key_cache_block_size;
+
+--echo throw errors in STRICT mode
+SET SQL_MODE=STRICT_ALL_TABLES;
+
+# sys_var_ulonglong_ptr: sys_max_binlog_cache_size
+--error ER_WRONG_VALUE_FOR_VAR
+SET @@global.max_binlog_cache_size=-1;
+
+# sys_var_thd_ha_rows: "max_join_size" et al.
+--error ER_WRONG_VALUE_FOR_VAR
+SET @@global.max_join_size=0;
+
+# sys_var_key_buffer_size: "key_buffer_size"
+--error ER_WARN_CANT_DROP_DEFAULT_KEYCACHE
+SET @@global.key_buffer_size=0;
+
+# sys_var_key_cache_long: "key_cache_block_size" et al.
+--error ER_WRONG_VALUE_FOR_VAR
+SET @@global.key_cache_block_size=0;
+
+--echo throw warnings in default mode
+SET SQL_MODE=DEFAULT;
+
+SET @@global.max_binlog_cache_size=-1;
+SET @@global.max_join_size=0;
+# this is an exception. since this is a new error/warning, let's stay
+# compatible with the upcoming 5.6.
+--error ER_WARN_CANT_DROP_DEFAULT_KEYCACHE
+SET @@global.key_buffer_size=0;
+SET @@global.key_cache_block_size=0;
+
+# cleanup
+SET @@global.max_binlog_cache_size=DEFAULT;
+SET @@global.max_join_size=DEFAULT;
+SET @@global.key_buffer_size=@kbs;
+SET @@global.key_cache_block_size=@kcbs;
+
 --echo End of 5.1 tests
 
 ###########################################################################

strings/CHARSET_INFO.txt

@@ -208,14 +208,11 @@ charpos()   - calculates the offset of the given position in the string.
               Used in SQL functions LEFT(), RIGHT(), SUBSTRING(), 
               INSERT()
 
-well_formed_length()
-            - finds the length of correctly formed multi-byte beginning.
-              Used in INSERTs to cut a beginning of the given string
-              which is
-              a) "well formed" according to the given character set.
+well_formed_len()
+            - returns length of a given multi-byte string in bytes
+              Used in INSERTs to shorten the given string so it
+              a) is "well formed" according to the given character set
               b) can fit into the given data type
-              Terminates the string in the good position, taking in account
-              multi-byte character boundaries.
 
 lengthsp()  - returns the length of the given string without trailing spaces.