More janitorial work

Install vpp api header files in /usr/include/vpp-api, instead of
/usr/include/api. Someone will eventually complain if we continue with
the status quo.

Generate /usr/bin/vpp_plugin_configure, to correctly configure
standalone plugin compilation against header files installed from the
dev package.

If a plugin's CFLAGS don't precisely match the installed vpp engine
binary, subtle misbehavior can and will occur. Example: the ip4/ip6
main_t structure size / member offsets depend on DPDK=[0|1]. Screw
that one up, and your brand-new configurable ip feature will
mysteriously fail to appear, even though the plugin loads perfectly.

Change-Id: I20c97fe1042808a79935863209d995c31953b98c
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/vpp-api/python/Makefile.am b/vpp-api/python/Makefile.am
index b96ff3d..4d2d221 100644
--- a/vpp-api/python/Makefile.am
+++ b/vpp-api/python/Makefile.am
@@ -33,11 +33,11 @@
 
 BUILT_SOURCES += vpp_papi.py
 
-vpp_papi.py: $(prefix)/../vpp/api/vpe.api pneum/api-gen.py
+vpp_papi.py: $(prefix)/../vpp/vpp-api/vpe.api pneum/api-gen.py
 	@echo "  PYTHON API";                                            	  \
 	$(CC) $(CPPFLAGS) -E -P -C -x c $<			                  \
 	| vppapigen --input - --python defs_$@;                                   \
-	echo "#include <api/vpe_msg_enum.h>"                                      \
+	echo "#include <vpp-api/vpe_msg_enum.h>"                                      \
 	| $(CC) $(CPPFLAGS) -E -P -x c - | grep VL_API                            \
 	| @srcdir@/pneum/api-gen.py -i defs_$@ > @srcdir@/vpp_papi/$@