Otherwise, the HTTP client might be destroyed before it has written all data, since the responses have already been received.

In particular this fixes http-test on Win32.

Fixes a recently introduced build error on Windows.

Microsoft's docs say to include either <process.h> or <stdlib.h>. I
arbitrarily chose process.h.

This allows functions which use KJ_EXPECT and other test macros to be built without linking libkj-test, which pulls in a possibly-unwanted main() function.

In particular, afl-testcase.c++ could not link in -fno-exceptions mode without this change.

I'm not really sure how Cap'n Proto has worked at all on GCC 5. For some reason this only ended up being tickled after e6e29122.

Fixes #442.

Fixes https://github.com/sandstorm-io/ekam/issues/13
Fixes https://github.com/sandstorm-io/ekam/issues/11

Since this header is included by everyone, and units.h has lots of templates, this seems like it could significantly improve build times.

Don't allow kj::maxValue / kj::minValue for Guarded types, since they'll break down when CAPNP_DEBUG_TYPES is off.

The problem with kj::range() is that if the inputs are not recognized as the same type, the typechecker can get annoyed.