OCD: foreach -> C++11 ranged for

src/download-via-ssh/download-via-ssh.cc

src/libexpr/attr-path.cc

src/libexpr/eval.cc

src/libexpr/get-drvs.cc

src/libexpr/names.cc

src/libexpr/nixexpr.cc

src/libexpr/parser.y

src/libexpr/primops.cc

src/libexpr/value-to-json.cc

src/libexpr/value-to-xml.cc

src/libstore/build.cc

src/libstore/derivations.cc

src/libstore/gc.cc

src/libstore/globals.cc

src/libstore/local-store.cc

src/libstore/misc.cc

src/libstore/optimise-store.cc

src/libstore/pathlocks.cc

src/libstore/references.cc

src/libstore/remote-store.cc