For asynchronous tests, the contract between test file and test runner
is implicit: runners are expected to inspect the source code for
references to a global `$DONE` identifier.

Promote a more explicit contract between test file and test runner by
introducing a new frontmatter "tag", `async`. This brings asynchronous
test configuration in-line with other configuration mechanisms and also
provides a more natural means of test filtering.

The modifications to test files was made programatically using the
`grep` and `sed` utilities:

    $ grep "\$DONE" test/ -r --files-with-match --null | \
        xargs -0 sed -i 's/^\(flags:\s*\)\[/\1[async, /g'
    $ grep "\$DONE" test/ -rl --null | \
        xargs -0 grep -E '^flags:' --files-without-match --null | \
        xargs -0 sed -i 's/^---\*\//flags: [async]\n---*\//'

add more tests of Promise.all

additional Promise test

add tests of Promise.prototype

add some tests for Promise.race

additional Promise tests

add Promise.reject and Promise.resolve tests

correct test description

rename badly-named files

use current license and minor style cleanup

correct understanding of undefined as thisArgument

incorporate line notes

Is this enough to make a constructor in ES6?

more accurate use of resolved,fulfilled etc.
remove some redundant tests
add new tests

remove "constant array" unclear language

better description

Update S25.4.2.1_A3.2_T1.js

address dangling ()

changes per @anba line notes
 - if GetIterator is abrupt, the Promise.race / Promise.all should reject
 - if Promise.race is called with nonconforming constructor as 'this',
   TypeError should be thrown (cannot reject if exeption is thrown from
   NewPromiseCapability; no promise exists yet...)

correct description of "this" testing in callbacks

fix whitespace, formatting

remove tab
add "next-turn" checking to sequencers