Conformance tests for array element type of tuple is union type of tuple element types
Tests to check equivalency of union types
A union type encompasses an unordered set of unrelated types (that is, types that aren’t subtypes of each other). The following rules govern union types:
•	A | B is equivalent to A if B is a subtype of A.
•	A | B is equivalent to B | A.
•	AB | C is equivalent to A | BC, where AB is A | B and BC is B | C.
Tests for source (S) of subtype is union type (U)
A union type U is a subtype of a type T if each type in U is a subtype of T
Tests for checking if type S is subtype of union type
T is a union type and S is a subtype of at least one constituent type of T
Tests for assignment compatibility of union types
•	A union type U is assignable to a type T if each type in U is assignable to T.
•	A type T is assignable to a union type U if T is assignable to any type in U.
Tests for union members:
If each type in U has a property P, U has a property P of a union type of the types of P from each type in U.
Tests for union of call signatures
If each type in U has call signatures and the sets of call signatures are identical ignoring return types, U has the same set of call signatures, but with return types that are unions of the return types of the respective call signatures from each type in U.
Tests for union of construct signatures

If each type in U has construct signatures and the sets of construct signatures are identical ignoring return types, U has the same set of construct signatures, but with return types that are unions of the return types of the respective construct signatures from each type in U.
Tests for union of index signatures:
•	If each type in U has a string index signature, U has a string index signature of a union type of the types of the string index signatures from each type in U.
•	If each type in U has a numeric index signature, U has a numeric index signature of a union type of the types of the numeric index signatures from each type in U.
Results of || operation produces union type
Tests for Conditional operator can generate union type
Tests for union type literals
A union type literal is written as a sequence of types separated by vertical bars.
UnionType:
PrimaryOrUnionType   |   PrimaryType
A union typle literal references a union type.
When function or constructor types are included in union types they must be enclosed in parentheses
Identity of union type
Array literal produces union type if the it is not contextually typed
Test cases of function infering return type of functions
if f is a contextually typed function expression (section 4.9.3), the inferred return type is the union type (section 3.3.4) of the types of the return statement expressions in the function body, ignoring return statements with no expressions.
Otherwise, the inferred return type is the first of the types of the return statement expressions in the function body that is a supertype (section 3.8.3) of each of the others, ignoring return statements with no expressions. A compile-time error occurs if no return statement expression has a type that is a supertype of each of the others.
Merge branch 'master' into unionTypeConformance
Merge pull request #1056 from Microsoft/unionTypeConformance

Union type conformance