configure: test(1) uses = not == for string comparison

Avoids a bash-ism.

Signed-off-by: Patrick Welche <prlw1@cam.ac.uk>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

m4/python_devel.m4

@@ -4,7 +4,7 @@ ac_previous_ldflags=$LDFLAGS
 ac_python_version=`$PYTHON -c 'import distutils.sysconfig; \
     print distutils.sysconfig.get_config_var("VERSION")'`
 AC_PATH_PROG([pyconfig], [$PYTHON-config], [no])
-AS_IF([test x"$pyconfig" == x"no"], [
+AS_IF([test x"$pyconfig" = x"no"], [
     dnl For those that don't have python-config
     CPPFLAGS="$CFLAGS `$PYTHON -c 'import distutils.sysconfig; \
         print "-I" + distutils.sysconfig.get_config_var("INCLUDEPY")'`"