Fix typo that prevents VPATH builds.

This commit was SVN r25201.

opal/mca/event/libevent207/configure.m4

@@ -178,7 +178,7 @@ EOF
            file=$basedir/libevent
            opal_event_libevent207_ADD_CPPFLAGS="-I$OMPI_TOP_SRCDIR/$file -I$OMPI_TOP_SRCDIR/$file/include"
            AS_IF([test "$OMPI_TOP_BUILDDIR" != "$OMPI_TOP_SRCDIR"],
-                 [opal_event_libevent207_ADD_CPPAFLAGS="$opal_event_libevent207_ADD_CPPFLAGS -I$OMPI_TOP_BUILDDIR/$file/include"])
+                 [opal_event_libevent207_ADD_CPPFLAGS="$opal_event_libevent207_ADD_CPPFLAGS -I$OMPI_TOP_BUILDDIR/$file/include"])
            if test "$with_devel_headers" = "yes" ; then
                opal_event_libevent207_ADD_WRAPPER_EXTRA_CPPFLAGS='-I${includedir}/openmpi/opal/mca/event/libevent207/libevent -I${includedir}/openmpi/opal/mca/event/libevent207/libevent/include'
            fi