libcoap-1.pc: fix pkg-config include path

This change excludes the coap subdirectory from the include path
reported by pkg-config --cflags to avoid name conflicts with other
installed packages. Applications now must add the prefix 'coap/'
to include directives for libcoap header files, e.g.

  #include <coap/coap.h>

Jean-Claude Michelou has reported this problem in Bug #82 [1].

[1] https://github.com/obgm/libcoap/issues/82

A minimal Makefile now could look be written as:

  PKG_LIBCOAP=libcoap-1
  CPPFLAGS=$(shell pkg-config --cflags-only-I $(PKG_LIBCOAP)) -DWITH_POSIX
  LDFLAGS=$(shell pkg-config --libs-only-L $(PKG_LIBCOAP))
  LDLIBS=$(shell pkg-config --libs-only-l $(PKG_LIBCOAP))

examples/Makefile.am

@@ -9,7 +9,7 @@
 if BUILD_EXAMPLES
 
 # picking up the default warning CFLAGS into AM_CFLAGS
-AM_CFLAGS = -isystem$(top_builddir)/include/coap -I$(top_srcdir)/include/coap $(WARNING_CFLAGS) -std=c99
+AM_CFLAGS = -isystem$(top_builddir)/include -I$(top_srcdir)/include $(WARNING_CFLAGS) -std=c99
 
 # etsi_iot_01 and tiny are missing
 bin_PROGRAMS = coap-client coap-server coap-rd

examples/client.c

@@ -23,7 +23,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 
-#include "coap.h"
+#include <coap/coap.h>
 #include "coap_list.h"
 
 int flags = 0;

examples/coap-rd.c

@@ -34,9 +34,9 @@
 #include <signal.h>
 
 #include "coap_config.h"
-#include "utlist.h"
-#include "resource.h"
-#include "coap.h"
+#include <coap/utlist.h>
+#include <coap/resource.h>
+#include <coap/coap.h>
 
 #define COAP_RESOURCE_CHECK_TIME 2
 

examples/coap-server.c

@@ -26,8 +26,8 @@
 #include <signal.h>
 
 #include "coap_config.h"
-#include "resource.h"
-#include "coap.h"
+#include <coap/resource.h>
+#include <coap/coap.h>
 
 #define COAP_RESOURCE_CHECK_TIME 2
 

examples/coap_list.c

@@ -13,8 +13,8 @@
 #include <stdio.h>
 #include <string.h>
 
-#include "debug.h"
-#include "mem.h"
+#include <coap/debug.h>
+#include <coap/mem.h>
 #include "coap_list.h"
 
 

examples/coap_list.h

@@ -11,7 +11,7 @@
 #ifndef _COAP_LIST_H_
 #define _COAP_LIST_H_
 
-#include "utlist.h"
+#include <coap/utlist.h>
 
 typedef struct coap_list_t {
   struct coap_list_t *next;

libcoap-1.pc.in

@@ -8,4 +8,4 @@ Description: C-Implementation of CoAP.
 Version: @PACKAGE_VERSION@
 URL: @PACKAGE_URL@
 Libs: -L${libdir} -lcoap-@LIBCOAP_API_VERSION@
-Cflags: -I${includedir}/coap
+Cflags: -I${includedir}