* configure.ac (APIVERSION): New substituted variable.

* configure.ac (APIVERSION): New substituted variable.
(pkgvdatadir): Ditto.  Versioned data directory.
(pkgvmacrodir): Ditto.  Versioned aclocal directory.
(LN): New check for LN command.
* Makefile.am (aclocal_DATA): Replaced with...
(pkgvmacro_DATA): ...this.
(install-data-local): Remove old shared resources.
(install-exec-hook): Make versioned links to executables.
(uninstall-hook): Remove versioned files.
* libltdl/Makefile.am (ltdldatadir): Redefine in terms of
pkgvdatadir.
* libltdl/loaders/Makefile.am (ltdldatadir): Ditto.
* libtoolize.m4sh: Copy macro files from versioned macro directory
instead of shared aclocal directory.
* doc/libtool.texi: Document it.
* NEWS: Updated.