Petitboot v1.7.1 tagged

[Samuel Mendoza-Jonas]

Petitboot v1.7.1 has been tagged, including a number of small fixes and a fixup
of a missed issue in v1.7.0:

- Set stdout-path property
	linux,stdout-path is technically deprecated in favour of stdout-path,
	but set both properties to support older and newer kernels.

- Several fixes for issues reported by clang / scan-build.
	Cheers to Joel Stanley for uncovering and patching these issues.

- Fix stale boot cancellation code
	The load_url_async() changes in v1.7.0 neglected to update the
	cancellation path in boot.c which could lead to a segfault on a
	cancelled boot.

- Fix gpg.h path
	A single character fix means `make dist` now succeeds - watch this
	space for tarball releases now.