python: Make Python detection more robust.

Previously, missing Python development packages made configure fail
instead of merely disabling the bindings.

* configure.ac: Check for 'PYTHON_VERSION'.
* m4/ax_python_devel.m4: Make test non-fatal.

Signed-off-by: Justus Winter <justus@g10code.com>

configure.ac

@@ -365,6 +365,16 @@ if test "$found" = "1"; then
     else
         AM_PATH_PYTHON([3.3])
         AX_SWIG_PYTHON
+	if test -z "$PYTHON_VERSION"; then
+           if test "$explicit_languages" = "1"; then
+              AC_MSG_ERROR([[
+***
+*** Please install the python development packages.
+***]])
+	    else
+                enabled_languages=$(echo $enabled_languages | sed 's/python//')
+            fi
+	fi
     fi
 fi
 

m4/ax_python_devel.m4

@@ -304,13 +304,12 @@ EOD`
 	AC_MSG_RESULT([$pythonexists])
 
         if test ! "x$pythonexists" = "xyes"; then
-	   AC_MSG_FAILURE([
+	   AC_MSG_WARN([
   Could not link test program to Python. Maybe the main Python library has been
   installed in some non-standard library path. If so, pass it to configure,
   via the LDFLAGS environment variable.
   Example: ./configure LDFLAGS="-L/usr/non-standard-path/python/lib"
   ============================================================================
-   ERROR!
    You probably have to install the development version of the Python package
    for your distribution.  The exact name of this package varies among them.
   ============================================================================