Fix for bug#41486: extra character appears in BLOB for every

~40Mb after mysqldump/import 
        
When the input string exceeds the maximum allowed size for the 
internal buffer, batch_readline() returns a truncated string. 
Since there was no way for a caller to determine whether the 
string was truncated or not, the command line client assumed 
batch_readline() to always return the whole input string and 
appended a newline character. This resulted in garbled data 
when importing dumps containing strings longer than the 
maximum input buffer size. 
  
Fixed by adding a flag to the batch_readline() interface to 
signal a truncated string to the caller. 
  
Other minor problems fixed during patch implementation: 
 
- The maximum allowed buffer size for batch_readline() was set 
up depending on the client's max_allowed_packet value. It does 
not actully make any sense, as those variables are not 
related. The input buffer size limit is now always set to 1 
MB. 
  
- fill_buffer() did not always set the EOF flag. 
 
- The input buffer could actually grow twice as the specified 
limit due to insufficient checks in intern_read_line().

mysql-test/r/mysql.result

@@ -192,4 +192,15 @@ delimiter
 1
 1
 1
+set @old_max_allowed_packet = @@global.max_allowed_packet;
+set @@global.max_allowed_packet = 2 * 1024 * 1024 + 1024;
+set @@max_allowed_packet = @@global.max_allowed_packet;
+CREATE TABLE t1(data LONGBLOB);
+INSERT INTO t1 SELECT REPEAT('1', 2*1024*1024);
+SELECT LENGTH(data) FROM t1;
+LENGTH(data)
+2097152
+DROP TABLE t1;
+set @@global.max_allowed_packet = @old_max_allowed_packet;
+set @@max_allowed_packet = @@global.max_allowed_packet;
 End of 5.0 tests