Merge branch 'it/fetch-pack-many-refs' into maint

When "git fetch" encounters repositories with too many references, the command line of "fetch-pack" that is run by a helper e.g. remote-curl, may fail to hold all of them. Now such an internal invocation can feed the references through the standard input of "fetch-pack". By Ivan Todoroski * it/fetch-pack-many-refs: remote-curl: main test case for the OS command line overflow fetch-pack: test cases for the new --stdin option remote-curl: send the refs to fetch-pack on stdin fetch-pack: new --stdin option to read refs from stdin Conflicts: t/t5500-fetch-pack.sh