The Manila hemp is derived from a species of banana originally from the Philippines, whose fibers are tough. The hemp is then used during the paper making process, similar to how Kraft paper uses wood pulp. So the mystery is solved, the manila envelope gets its name from the hemp in which it is made from.
No country currently backs its currency with gold, but many have in the past, including the U.S.; for half a century beginning in 1879, Americans could trade in $20.67 for an ounce of gold. The country effectively abandoned the gold standard in 1933, and completely severed the link between the dollar and gold in 1971.