Python: add am_cv_python_includes to override runtime python-config check
[Gustavo: update for dbus-python 1.2.0]

diff -Nura dbus-python-1.2.0.orig/configure dbus-python-1.2.0/configure
--- dbus-python-1.2.0.orig/configure	2013-05-08 04:48:42.000000000 -0300
+++ dbus-python-1.2.0/configure	2014-07-03 16:54:25.922727033 -0300
@@ -11762,6 +11762,12 @@
 else
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for Python headers using $PYTHON-config --includes" >&5
 $as_echo_n "checking for Python headers using $PYTHON-config --includes... " >&6; }
+if test "${am_cv_python_includes+set}" = set; then
+  $as_echo_n "(cached) $ECHO_C" >&6
+  PYTHON_INCLUDES=${am_cv_python_includes}
+  { $as_echo "$as_me:$LINENO: result: $PYTHON_INCLUDES" >&5
+$as_echo_t "${ECHO_T}$PYTHON_INCLUDES" >&6; }
+else
   PYTHON_INCLUDES=`$PYTHON-config --includes`
   if test $? = 0; then
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PYTHON_INCLUDES" >&5
@@ -11781,6 +11787,7 @@
 $as_echo "$PYTHON_INCLUDES" >&6; }
   fi
 fi
+fi
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether those headers are sufficient" >&5
 $as_echo_n "checking whether those headers are sufficient... " >&6; }