Fix nits and bugs in tests `help*.test'. * tests/help4.test: Fix broken sed commands used to strip `-W...' flags away from "$AUTOMAKE" and "$ACLOCAL". * tests/help3.test: Likewise, and fix a botched comment. * tests/help.test: Likewise. Also, use "AUTOMAKE_fails ..." instead of "$AUTOMAKE ... && Exit 1", for consistency and to please maintainet-check. * tests/help2.test: Likewise.