Nested automake conditionals don't work

Nested automake conditionals don't work

	* configure.ac (ENABLE_ZIP_ARCHIVE_AND_CXX11): Define this
	automake condition variable that is true if both the zip archive
	and c++11 features are enabled.  This is important to know if the
	test runtestdot is going to be compiled.  That test needs both
	c++11 and the zip archive features.
	* tests/Makefile.am: Do not nest automake conditional statements.
	It does not work.  Rather, use the new
	ENABLE_ZIP_ARCHIVE_AND_CXX11 condition variable.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>