[pygi] Fix warning in configure.

[Tomeu Vizoso <tomeuv src gnome org>]

commit 71a2148b00dfdda99e0d961ae39b901608724e59
Author: Steve Frécinaux <code istique net>
Date:   Fri May 21 19:05:03 2010 +0200

    Fix warning in configure.
    
    The warning is caused by the use of the construction 'CFLAGS+=' in a
    sh version that doesn't understand it (in this case, 'dash').
    
    https://bugzilla.gnome.org/show_bug.cgi?id=619311

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 738b1d5..f503818 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,7 +29,7 @@ PYTHON_INCLUDES=`$PYTHON_CONFIG --includes`
 AC_SUBST(PYTHON_INCLUDES)
 
 save_CPPFLAGS="${CPPFLAGS}"
-CPPFLAGS+="${PYTHON_INCLUDES}"
+CPPFLAGS="${CPPFLAGS} ${PYTHON_INCLUDES}"
 AC_CHECK_HEADER(Python.h, , AC_MSG_ERROR(Python headers not found))
 CPPFLAGS="${save_CPPFLAGS}"