cargo-snapshot.inc: use a date-specific downloadfilename

This allows the snapshot to be cached in a local mirror with a unique
name

recipes-devtools/cargo/cargo-snapshot.inc

@@ -1,4 +1,4 @@
 
-CARGO_SNAPSHOT = "2016-01-31/cargo-nightly-x86_64-unknown-linux-gnu.tar.gz"
+CARGO_SNAPSHOT = "2016-01-31/cargo-nightly-x86_64-unknown-linux-gnu.tar.gz;downloadfilename=cargo-nightly-x86_64-unknown-linux-gnu-2016-01-31.tar.gz"
 SRC_URI[md5sum] = "52f48780b7cfadc88813766048d4d402"
 SRC_URI[sha256sum] = "1920e661bab536eba763ff6704a1d62fb20bb0f67d8c5a119e41c49510ea5fa6"

recipes-devtools/cargo/cargo.inc

@@ -54,7 +54,7 @@ do_compile () {
 
 	rm -rf target/snapshot
 	mkdir -p target
-	cp -R ${WORKDIR}/$(basename ${CARGO_SNAPSHOT} .tar.gz)/cargo target/snapshot
+	cp -R ${WORKDIR}/cargo-nightly-x86_64-unknown-linux-gnu/cargo target/snapshot
 
 	oe_runmake ARGS="--verbose"
 }