[glom] Add a hint about building with Python 3

[Murray Cumming <murrayc src gnome org>]

commit a36ecd1e359119994949e0fde2f7e935efb68fab
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Sep 11 20:56:31 2013 +0200

    Add a hint about building with Python 3

 configure.ac |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 754d23e..ed46277 100644
--- a/configure.ac
+++ b/configure.ac
@@ -226,11 +226,17 @@ AM_PATH_PYTHON
 
 # Get the compiler and linker flags for embedding Python.
 # To specify a particular python version set an environment variable.
-# For instance: PYTHON=python2.5
+# For instance: PYTHON=python3.3
 # See http://www.gnu.org/software/autoconf-archive/ax_python_devel.html
-AX_PYTHON_DEVEL
+AX_PYTHON_DEVEL(>= '3.0.0')
 
 # Get the CFLAGS and LIBS for boost::python.
+# To use a non-default Boost::Python library, for instance to use
+# the version for Python3, if you already have set PYTHON=python3.3,
+# you'll need to pass something like this to configure to make it
+# link to the correct library (Yes, this is tedious).
+#   --with-boost-python=boost_python-mt-py33
+#
 # See http://www.gnu.org/software/autoconf-archive/ax_boost_base.html
 AX_BOOST_BASE
 # See http://www.gnu.org/software/autoconf-archive/ax_boost_python.html