Install headers to correct place, and try to detect if C++11 was not enabled.

c++/Makefile.am

@@ -39,7 +39,9 @@ MAINTAINERCLEANFILES =   \
 maintainer-clean-local:
 	-rm -rf build-aux
 
-nobase_include_HEADERS =                                       \
+includecapnpdir = $(includedir)/capnproto
+
+includecapnp_HEADERS =                                         \
   src/capnproto/macros.h                                       \
   src/capnproto/type-safety.h                                  \
   src/capnproto/blob.h                                         \

c++/src/capnproto/macros.h

@@ -26,6 +26,12 @@
 
 #include <inttypes.h>
 
+#ifdef __GNUC__
+#ifndef __GXX_EXPERIMENTAL_CXX0X__
+#warning Did you forget to enable C++11?  Make sure to pass -std=gnu++11 to GCC.
+#endif
+#endif
+
 namespace capnproto {
 
 #define CAPNPROTO_DISALLOW_COPY(classname) \