Fix build outside of srcdir

I don't know why 'distcheck' succeeded -- may be a bug there!

Author: bjori

config.m4

@@ -406,10 +406,12 @@ dnl }}}
 
   PHP_ADD_INCLUDE([$ext_srcdir/src/BSON/])
   PHP_ADD_INCLUDE([$ext_srcdir/src/MongoDB/])
+  PHP_ADD_INCLUDE([$ext_srcdir/src/Exception/])
   PHP_ADD_INCLUDE([$ext_srcdir/src/contrib/])
   PHP_ADD_INCLUDE([$ext_srcdir/src/libmongoc/src/mongoc/])
   PHP_ADD_BUILD_DIR([$ext_builddir/src/BSON/])
   PHP_ADD_BUILD_DIR([$ext_builddir/src/MongoDB/])
+  PHP_ADD_BUILD_DIR([$ext_builddir/src/Exception/])
   PHP_ADD_BUILD_DIR([$ext_builddir/src/contrib/])
   PHP_ADD_BUILD_DIR([$ext_builddir/src/libmongoc/src/mongoc/])
   if test "$PHP_LIBBSON" == "no"; then