Rename and consolidate tests in keywords directory

test/language/keywords/ident-ref-break.js

test/language/keywords/ident-ref-case.js

test/language/keywords/ident-ref-catch.js

test/language/keywords/ident-ref-continue.js

test/language/keywords/ident-ref-default.js

test/language/keywords/ident-ref-delete.js

test/language/keywords/ident-ref-do.js

test/language/keywords/ident-ref-else.js

test/language/keywords/ident-ref-finally.js

test/language/keywords/ident-ref-for.js

test/language/keywords/ident-ref-function.js

test/language/keywords/ident-ref-if.js

test/language/keywords/ident-ref-in.js

test/language/keywords/ident-ref-instanceof.js

test/language/keywords/ident-ref-new.js

test/language/keywords/ident-ref-return.js

test/language/keywords/ident-ref-switch.js

test/language/keywords/ident-ref-this.js

test/language/keywords/ident-ref-throw.js

test/language/keywords/ident-ref-try.js