[binutils-gdb] Fix PR gdb/19637: bound_registers.py: Add support for Python 3

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 7503099f3e29739d34cb1224d54fba96404e6e61 ***

Author: Jonah Graham <jonah@kichwacoders.com>
Branch: master
Commit: 7503099f3e29739d34cb1224d54fba96404e6e61

Fix PR gdb/19637: bound_registers.py: Add support for Python 3

Fix this the same way gdb/python/lib/gdb/printing.py handles it.

gdb/Changelog:
2017-03-17  Jonah Graham  <jonah@kichwacoders.com>

	PR gdb/19637
	* python/lib/gdb/printer/bound_registers.py: Add support for
	Python 3.