[oe] Correct versioning of unversioned source in git

[Tomas Novotny]

	Hi all,

there is a recipe sunxi-board-fex in meta-sunxi layer. That recipe fetches
sources from unversioned git which contains definitions of some boards (in
fact it is something like a store).
	I'm not sure with correct versioning in OE. Is that:
PV = "1.0+git${SRCPV}"
SRCREV = "<some_gitrev_I_want>"
correct? Will be change of SRCREV (only) catched by build system (I'm curious
how OE handles age of the rev in git)?
	Or do I need to raise PV to 1.1 and so on with every change to SRCREV?
	Thanks,

	Tomas