improved way to find the necessary include path, even if module writers did a sloppy job

ax_init_standard_project.m4

@@ -373,68 +373,16 @@ EOF
 AC_DEFUN([AX_PKG_REQUIRE], [
   PKG_PROG_PKG_CONFIG
   PKG_CHECK_MODULES([$1], [$2], [
-    if test -n "$3"; then
-      $1_found=0;
-      for p in ${$1_CFLAGS}; do
-        if test -e ${p#-I}/$3; then
-          $1_found=1
-          break
-        fi
-      done
-      if test ${$1_found} -eq 0 -a -n "$3"; then
-        for p in "/usr/include" ${$1_CFLAGS}; do
-          AC_MSG_NOTICE([checking: [${p}] with [${p#-I}]])
-          $1_file=$(find ${p#-I} -name $(echo "$3" | sed 's,.*/,,') | grep "$3" | head -1)
-          AC_MSG_NOTICE([call: $1_file=[\$](find [$]{p[#]-I} -name "$3")])
-          AC_MSG_NOTICE([found: ${$1_file}])
-          if test -e "${$1_file}"; then
-            AC_MSG_NOTICE([Header file $3 found in sub path of $2 as ${$1_file}])
-            $1_CFLAGS="${$1_CFLAGS} -I${$1_file%/$3}"
-            $1_found=1
-            break
-          fi
-        done
-      fi
-      if test ${$1_found} -eq 0; then
-        AC_MSG_ERROR([Header file $3 not found in $2 with $1_CFLAGS = ${$1_CFLAGS}])
-      fi
-    fi
-    AM_CPPFLAGS+=" ${$1_CFLAGS}"
-    AM_CXXFLAGS+=" ${$1_CFLAGS}"
-    LIBS+=" ${$1_LIBS}"
     PKG_REQUIREMENTS+=" $2"
   ], [
     if test -n "$4"; then
       AC_MSG_WARN([Recommended package $2 for feature $1 not installed, trying $4])
+      $1_found=0
       for pkg in $4; do
         PKG_CHECK_MODULES([$1], [$pkg], [
-          if test -n "$3"; then
-            $1_found=0;
-            for p in ${$1_CFLAGS}; do
-              if test -e ${p#-I}/$3; then
-                $1_found=1
-                break
-              fi
-            done
-            if test ${$1_found} -eq 0; then
-              for p in /usr/include ${$1_CFLAGS}; do
-                $1_file=$(find ${p#-I} -name $(echo "$3" | sed 's,.*/,,') | grep "$3" | head -1)
-                if test -e ${$1_file}; then
-		  AC_MSG_NOTICE([Header file $3 found in sub path of ${pkg} as ${$1_file}])
-                  $1_CFLAGS="${$1_CFLAGS} -I${$1_file%/$3}"
-                  $1_found=1
-                  break
-                fi
-              done
-            fi
-            if test ${$1_found} -eq 0; then
-              AC_MSG_WARN([Header file $3 not found in ${pkg} with $1_CFLAGS = ${$1_CFLAGS}])
-            fi
-          fi
-          AM_CPPFLAGS+=" ${$1_CFLAGS}"
-          AM_CXXFLAGS+=" ${$1_CFLAGS}"
-          LIBS+=" ${$1_LIBS}"
           PKG_REQUIREMENTS+=" $pkg"
+          $1_found=1
+          break;
         ], [
           AC_MSG_WARN([Recommended package $pkg for feature $1 not installed])
         ])
@@ -442,6 +390,8 @@ AC_DEFUN([AX_PKG_REQUIRE], [
       if test ${$1_found} -eq 0; then
         AC_MSG_ERROR([Required package $2 or $4 for feature $1 not installed])
       fi
+    else
+      AC_MSG_ERROR([Required package $2 for feature $1 not installed])
     fi
   ])
   AC_SUBST(AM_CPPFLAGS)
@@ -452,12 +402,30 @@ AC_DEFUN([AX_PKG_REQUIRE], [
     CPPFLAGS=" ${$1_CFLAGS} ${CPPFLAGS}"
     AC_CHECK_HEADER([$3], [
     ], [
-      AC_MSG_ERROR([Required header $3 for feature $1 not found])
+      $1_found=0
+      for x in ${$1_CFLAGS}; do
+        AC_MSG_NOTICE([search for $3 in ${x[#]-I}])
+        for f in $(find ${x[#]-I} -name "$3"); do
+          if test -f "$f"; then
+            $1_found=1
+            $1_CFLAGS+=" -I${f%/*}"
+            AC_MSG_NOTICE([added path ${f%/*}])
+            break;
+          fi
+        done
+        if test ${$1_found} -eq 1; then
+          break;
+        fi
+      done
+      if test ${$1_found} -eq 0; then
+        AC_MSG_ERROR([Required header $3 for feature $1 with ${$1_CFLAGS} not found])
+      fi
     ])
     CPPFLAGS=${old_CPPFLAGS}
-  elif test ${$1_found} -eq 0; then
-    AC_MSG_ERROR([Required package $2 for feature $1 not installed])
   fi
+  AM_CPPFLAGS+=" ${$1_CFLAGS}"
+  AM_CXXFLAGS+=" ${$1_CFLAGS}"
+  LIBS+=" ${$1_LIBS}"
 ])
 
 # check if a specific package exists