List src/include/partitioning in src/include/Makefile

This omission prevented partitioning header files from being installed.

Per buildfarm member crake.

src/include/Makefile

@@ -19,8 +19,9 @@ all: pg_config.h pg_config_ext.h pg_config_os.h
 # Subdirectories containing installable headers
 SUBDIRS = access bootstrap catalog commands common datatype \
 	executor fe_utils foreign \
-	lib libpq mb nodes optimizer parser postmaster regex replication \
-	rewrite statistics storage tcop snowball snowball/libstemmer tsearch \
+	lib libpq mb nodes optimizer parser partitioning postmaster \
+	regex replication rewrite \
+	statistics storage tcop snowball snowball/libstemmer tsearch \
 	tsearch/dicts utils port port/atomics port/win32 port/win32_msvc \
 	port/win32_msvc/sys port/win32/arpa port/win32/netinet \
 	port/win32/sys portability