Compiler warnings due to non-matching conversion
specifications in format strings in DBUG_PRINT calls,
due to non-used parameters (in non-debug mode), and
due to seemingly uninitialized variables.

Initialized variables, declared parameters unused, and
casted DBUG_PRINT arguments to get rid of warnings.


myisam/mi_range.c:
  Bug#25213 - Compiler warnings in MyISAM code
  Initialized a variable to get rid of a compiler warning.
myisam/mi_test1.c:
  Bug#25213 - Compiler warnings in MyISAM code
  Declared an parameter unused to get rid of warnings.
myisam/mi_write.c:
  Bug#25213 - Compiler warnings in MyISAM code
  Initialized a variable to get rid of a compiler warning.
  Casted arguments to DBUG_PRINT to match them with their
  format string conversion specification.
myisam/rt_split.c:
  Bug#25213 - Compiler warnings in MyISAM code
  Initialized variables to get rid of compiler warnings.