Do not pass top_srcdir to configure scripts in testsuite.
* tests/autotest.at (srcdir propagation): Copy install-sh to
source tree.
(my only test): Drop setting of `top_srcdir'.
* tests/base.at (Input/Output): Likewise.
* tests/local.at (AT_CONFIGURE_AC): Copy install-sh,
config.guess, and config.sub to test source tree.
Drop AC_CONFIG_AUX_DIR setting.
(AT_CHECK_CONFIGURE): Drop setting of `top_srcdir'.
* tests/torture.at (Substitute a 2000-byte string): Drop
AC_CONFIG_AUX_DIR setting, copy install-sh to test source tree.
(Substitute a newline, datarootdir workaround): Likewise.
(Define a newline): Adjust for linenumber changes in configure.ac.
* tests/foreign.at (Libtool): Adjust comment to reflect changes.