mi: Use the value in mi_console_file->quote as the quoting character

In mi_interpreter_init, multiple MI consoles/channels are created and a quoting
character is given.  In mi_console_raw_packet, we check if the value is not 0
to decide if we should quote the string, but we don't use the value. It is
hardcoded to ".  We might never use another quoting character than an actual
quote, but I suggest we change it, for correctness.  There is not visible
behavior change.

I changed the latest fputs_unfiltered changed to fputc_unfiltered just to stay
consistent.

gdb/ChangeLog:

2014-05-12  Simon Marchi  <simon.marchi@ericsson.com>

	* mi/mi-console.c (mi_console_raw_packet): Use the value from
	mi_console->quote as the quoting character.