configure.ac: make it more portable.

configure.ac: make it more portable.

===> Creating toolchain wrappers for gnunet-0.11.0pre66
===> Configuring for gnunet-0.11.0pre66
=> Modifying GNU configure scripts to avoid --recheck
=> Replacing config-guess with pkgsrc versions
=> Replacing config-sub with pkgsrc versions
=> Replacing install-sh with pkgsrc version
=> Checking for portability problems in extracted files
ERROR: [check-portability.awk] => Found test ... == ...:
ERROR: [check-portability.awk] configure:     if test "x$enable_autostart" == "xno"

Explanation:
===========================================================================
The "test" command, as well as the "[" command, are not required to know
the "==" operator. Only a few implementations like bash and some
versions of ksh support it.

When you run "test foo == foo" on a platform that does not support the
"==" operator, the result will be "false" instead of "true". This can
lead to unexpected behavior.

There are two ways to fix this error message. If the file that contains
the "test ==" is needed for building the package, you should create a
patch for it, replacing the "==" operator with "=". If the file is not
needed, add its name to the CHECK_PORTABILITY_SKIP variable in the
package Makefile.
===========================================================================

*** Error code 1

Stop.
make[1]: stopped in /usr/pkgsrc/wip/gnunet
*** Error code 1