AU_ALIAS was removed because the new version is incompatible
with the old version.

It no longer checks for <sys/capability.h> separately.
It's enough to test for it as part of AC_CHECK_DECL.
The defines HAVE_CAPSICUM_SYS_CAPSICUM_H and
HAVE_CAPSICUM_SYS_CAPABILITY_H were removed as unneeded.
HAVE_SYS_CAPSICUM_H from AC_CHECK_HEADERS is enough.

It no longer does a useless search for the Capsicum library
if the header wasn't found.

Fixed a bug in ACTION-IF-FOUND (the first argument). Specifying
the argument omitted the default action but the given action
wasn't used instead.

AC_DEFINE([HAVE_CAPSICUM]) is now always called when Capsicum
support is found. Previously it was part of the default
ACTION-IF-FOUND which a custom action would override. Now
the default action only prepends ${CAPSICUM_LIB} to LIBS.

The documentation was updated.

Since there as no serial number, "#serial 2" was added.