aclocal: trace AC_CONFIG_MACRO_DIR_TRACE
This is now the documented way, and indeed the only correct way, to
support AC_CONFIG_MACRO_DIR and AC_CONFIG_MACRO_DIRS in third-party
tools. See autoconf commit v2.69-45-g5269030 of 2012-11-09,
"AC_CONFIG_MACRO_DIRS: improve tracing and add sanity checks".
* aclocal.in (trace_used_macros): Trace 'AC_CONFIG_MACRO_DIR_TRACE'
rather than 'AC_CONFIG_MACRO_DIRS'. We still have to trace
'AC_CONFIG_MACRO_DIR' explicitly though, for compatibility with
Autoconf versions before 2.70.
* t/aclocal-macrodirs.tap: Enhance w.r.t. precedence of arguments
in one and several AC_CONFIG_MACRO_DIRS calls.
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>