Changes to build system ; automatic detection of runtime native jpl code

Change build.xml to use ivy to download dependencies. 

Only available JPL jar in maven repository is 
     http://mvnrepository.com/artifact/jpl/jpl/3.1.4-alpha .

This is old enough that the repository still points to CVS space; however, the version in the swipl  git HEAD still thinks it's 3.1.4-alpha, so it's hard to say it's outdated.  It definitely seems to work ok with SWI-Prolog version 6.3.10 for x86_64-darwin11.4.2, and the JPL docs haven't changed for quite some time.  

Change AceLocal to automatically locate native JPL extension using "swipl --dump-runtime-variables".

The build file could be modified to fetch the jar file from the swipl install dir using a similar mechanism.