WL#1895 - Print message to error log in case of detected MyISAM corruption

Changed my_error() to print error messages, which come from
arbitrary registered ranges of error messages. Messages can
be unregistered (and should be at end of the program).
Added registration of handler error messages.
Added a new mi_print_error() macro and a new 
mi_report_error() function, which supply error
messages with a table name.
Added calls to mi_print_error() or mi_report_error()
at all places in MyISAM, where table corruption is detected.

mysql-test/r/merge.result

@@ -178,9 +178,9 @@ t3	CREATE TABLE `t3` (
 ) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1 UNION=(`t1`,`t2`)
 create table t4 (a int not null, b char(10), key(a)) engine=MERGE UNION=(t1,t2);
 select * from t4;
-ERROR HY000: Can't open file: 't4.MRG' (errno: 143)
+ERROR HY000: All tables in the MERGE table are not identically defined
 alter table t4 add column c int;
-ERROR HY000: Can't open file: 't4.MRG' (errno: 143)
+ERROR HY000: All tables in the MERGE table are not identically defined
 create database mysqltest;
 create table mysqltest.t6 (a int not null primary key auto_increment, message char(20));
 create table t5 (a int not null, b char(20), key(a)) engine=MERGE UNION=(test.t1,mysqltest.t6);

mysql-test/r/repair.result

@@ -31,7 +31,7 @@ create table t1 engine=myisam SELECT 1,"table 1";
 flush tables;
 repair table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	repair	error	Can't open file: 't1.MYI' (errno: 130)
+test.t1	repair	error	Incorrect file format 't1'
 repair table t1 use_frm;
 Table	Op	Msg_type	Msg_text
 test.t1	repair	warning	Number of rows changed from 0 to 1

mysql-test/t/merge.test

@@ -47,9 +47,9 @@ show create table t3;
 
 # The following should give errors
 create table t4 (a int not null, b char(10), key(a)) engine=MERGE UNION=(t1,t2);
---error 1016
+--error 1168
 select * from t4;
---error 1016
+--error 1168
 alter table t4 add column c int;
 
 #