Erroneous backtrace on AVR.

	PR backtrace/16721
	PR backtrace/16832
	* avr-tdep.c (struct gdbarch_tdep): Mention avrxmega in the comment.
	(avr_gdbarch_init): Add xmega architectures given by bfd_architecture
	when setting the size of call_length.
	(avr_scan_prologue): Accept push r1 instruction for small stack
	allocation.
	* MAINTAINERS (Write After Approval): Add "Pierre Langlois".
Automatic date update in version.in