Add new parameter to do_eval so that only unescaped variables in input string is expanded and rest of string is left untouched.


client/mysqltest.c:
  Add new parameter to 'do_eval' that will add any escape chars found in the input string to the output string. 
  This is used in 'do_system' and in 'do_exec' where only unescaped variables
  will be expanded, rest of the string will be left untouched.
mysql-test/r/mysqltest.result:
  Update test result
mysql-test/t/mysqldump.test:
  Revert previous patch that added extra \\ in "exec" command
mysql-test/t/mysqltest.test:
  Revert previous patch that added extra \\ in exec command