Simplify the handle_md_command routine in target.c:

 - fix buffer overrun in mdw; final '\0' would overflow the output buffer.
 - return ERROR_COMMAND_SYNTAX_ERROR instead of ERROR_OK if:
   - less than one argument is provided
   - the command is called with a name other than mdb, mdh, or mdw.
 - factor all command output into new handle_md_output function


git-svn-id: svn://svn.berlios.de/openocd/trunk@1958 b42882b7-edfa-0310-969c-e2dbd0fdcd60