* Remove some of the obsolete macros.
* Use AC_CONFIG_MACRO_DIR to allow compatibility with older versions of
autoconf.
* Remove AU_ALIAS from curses macro.
On FreeBSD variant, readline functionality is provided by editline which
is almost compatible but not quite. We could do a specific check for
editline but if editline adds the functionality in the future, this
check will still continue to fail. Instead look for one of the symbols
currently missing in editline as a sanity check.
The macro does not track the include directory when it is passed in
using the '--with-readline=/foo/bar' invocation of '--with-readline'
flag.
This change should fix the problem. I've tried to keep the functionality
exactly the same as before and converted the script to pure M4sh, which
should produce a more portable configure script.
