C arrays are not default-initialized with NewArray

[losvald]

In Scala, new Array[T](size) has the semantics of filling the array with 0/null. However, the generated C code generates only a call to malloc, which creates an uninitialized array. For C++, we should generate new R[size]() where R is the remapped type, which calls the default-initializer (because of '()'). To be compatible with C, perhaps we should generate something like static R defaultVal; for (size_t i = 0; i < size; ++i) a[i] = defaultValue; for the general case and memset for the array of primitives?