svn configure doesn't see right python includes

I have several versions of python on my system ( 1.5, 2.1 2.2 and 2.3 ). I
compile SWIG 1.3.21 for usage with Python 2.3, but svn's configure script is
still confused and uses includes from another version:

configure: Enabled swig binding: python
checking for swig... /usr/local/bin/swig
checking swig version... 1.3.21
checking for swig library directory... /usr/local/lib/swig1.3
configure: "Configuring python swig binding"
checking if swig needs -L for its libraries... -L/usr/local/lib
checking for Python includes... -I/usr/include/python2.1
checking for compiling Python extensions... gcc -g -O2 -Wall -Wstrict-prototypes
-fPIC
checking for linking Python extensions... gcc -shared

It looks like it doesn't affect good operation of the bindings though (provided
you correctly jump through all the annoying hoops to get them right, like issue
1125 and make runtime in SWIG).

Original issue reported by timot