This is a first cut of the generalization of <available> and
<uptodate> that is on the list for Ant2. This task supports a single
condition and sets a property if it holds true - conditions can be
containers for other conditions in turn, giving it the opportunity to
support boolean logic.

Built in conditions as of now:

* <available> and <uptodate> (slightly modified the tasks to allow them to
be used as conditions)

* containers <and>, <or> and <not>

* New conditions <equals> (compares to Strings) and <os> which should
give easier access to os.name.

More extensive documentation to follow.  Take a look at Ant's build
file, it uses the task to detect whether javamail is available now.

I had to perform some ugly tricks to make sure that project gets
passed to every object that will need it - this will be very different
in the future I hope.


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@269456 13f79535-47bb-0310-9956-ffa450edef68