Merge pull request #410 from harrishancock/msvc-fixes

Fix MSVC build errors

c++/src/kj/array.h

@@ -524,7 +524,7 @@ struct Mapper {
     }
     return builder.finish();
   }
-  typedef decltype(*(array).begin()) Element;
+  typedef decltype(*kj::instance<T>().begin()) Element;
 };
 
 template <typename T, size_t s>

c++/src/kj/async-io.c++

@@ -122,7 +122,7 @@ private:
     auto partPtr = part.asPtr();
     parts.add(kj::mv(part));
     return input.tryRead(partPtr.begin(), partPtr.size(), partPtr.size())
-        .then([this,partPtr,total](size_t amount) -> Promise<uint64_t> {
+        .then([this,KJ_CPCAP(partPtr),total](size_t amount) -> Promise<uint64_t> {
       uint64_t newTotal = total + amount;
       if (amount < partPtr.size()) {
         return newTotal;