The sources tree has precedence over installed files when including headers

src/Makefile

@@ -4,7 +4,7 @@ PREFIX	= /usr/local
 DESTDIR	= 
 BINDIR	= $(PREFIX)/bin
 CC	= cc
-CPPFLAGSF= -I $(PREFIX)/include -I ../include
+CPPFLAGSF= -I ../include -I $(PREFIX)/include
 CPPFLAGS=
 CFLAGSF	= -W `pkg-config gtk+-2.0 --cflags`
 CFLAGS	= -Wall -g -O2 -pedantic

src/project.conf

@@ -1,6 +1,6 @@
 subdirs=applets
 targets=panel,run
-cppflags_force=-I $(PREFIX)/include -I ../include
+cppflags_force=-I ../include -I $(PREFIX)/include
 #cppflags=-D EMBEDDED
 cflags_force=-W `pkg-config gtk+-2.0 --cflags`
 cflags=-Wall -g -O2 -pedantic