Simplify inclusion of local jansson headers

src/Makefile.am

@@ -1,24 +1,20 @@
 SUBDIRS	= jansson-2.6
 
 ACLOCAL_AMFLAGS = -I m4
-JANSSON_CPPFLAGS= -I$(top_builddir)/src/jansson-2.6/src -I$(top_srcdir)/src/jansson-2.6/src
+AM_CPPFLAGS =  -I$(top_srcdir)/src/jansson-2.6/src
 
 lib_LTLIBRARIES = libckpool.la
-libckpool_la_CPPFLAGS = $(JANSSON_CPPFLAGS)
 libckpool_la_SOURCES = libckpool.c libckpool.h sha2.c sha2.h
 libckpool_la_LIBADD = @PTHREAD_LIBS@ @MATH_LIBS@ @RT_LIBS@
 
 bin_PROGRAMS = ckpool ckpmsg ckdb
-ckpool_CPPFLAGS = $(JANSSON_CPPFLAGS)
 ckpool_SOURCES = ckpool.c ckpool.h generator.c generator.h bitcoin.c bitcoin.h \
 		 stratifier.c stratifier.h connector.c connector.h uthash.h \
 		 utlist.h
 ckpool_LDADD = libckpool.la @JANSSON_LIBS@
 
-ckpmsg_CPPFLAGS = $(JANSSON_CPPFLAGS)
 ckpmsg_SOURCES = ckpmsg.c
 ckpmsg_LDADD = libckpool.la @JANSSON_LIBS@
 
-ckdb_CPPFLAGS = $(JANSSON_CPPFLAGS)
 ckdb_SOURCES = ckdb.c klist.c ktree.c klist.h ktree.h
 ckdb_LDADD = libckpool.la @JANSSON_LIBS@ @PQ_LIBS@