if the standard input is a directory.

The problem is that mysql monitor try to read from stdin without
checking input source type.

The solution is to stop reading data from standard input if a call
to read(2) failed.

A new test case was added into mysql.test.

client/my_readline.h:
  Data members error and truncated was added to LINE_BUFFER structure.
  These data members used instead of out parameters in functions
  batch_readline, intern_read_line.
client/mysql.cc:
  read_and_execute() was modified: set status.exit_status to 1
  when the error occured while reading the next command line in
  non-interactive mode. Also the value of the truncated attribute
  of structure LINE_BUFF is taken into account only for non-iteractive mode.
client/readline.cc:
  intern_read_line() was modified: cancel reading from input if
  fill_buffer() returns -1, e.g. if call to read failed.
  batch_readline was modified: set the error data member of LINE_BUFFER
  structure to value of my_errno when system error happened during call
  to my_read/my_realloc.
mysql-test/t/mysql.test:
  Test for bug#57450 was added.