Add missing include to BasicEnvironmentTestHelper

std::move requires <utility>.
Remove Catch submodule

Using a submodule seems to be an overkill... We are going to include
only indispensable files from external libraries.
Add (part of) Boost library

The Boost format library and its dependencies are added.
Use ustar format for dist

Now that we have the Boost library, we need to use an archive format
that supports long pathnames.
Add TESTHEADERS variable to Makefile.ac

Header files that are used for testing only are now explicitly
categorized. It was confusing for these headers declared in arbitrary
*_SOURCES variables.
Add Message template class
Change addDiagnosticMessage argument type to Message

With String, we cannot translate the diagnostic message later.
Make CLocaleEnvironmentStub inherit BasicEnvironmentStub virtually
Add DiagnosticMessage class
Add DiagnosticMessageTestHelper
Add DiagnosticEnvironmentStub class