MaxOS fixes

Avoid a thread deadlock
improvements to SWI predicates.
make variables_in_term system builtin.


git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@2304 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

changes-5.1.html

@@ -17,6 +17,8 @@
 
 <h2>Yap-5.1.4:</h2>
 <ul>
+<li> .</li>
+<li> NEW: X is random(Int) (SWI compatibility).</li>
 <li> NEW: seletchk/3.</li>
 <li> FIXED: do meta-expansion from undefp.</li>
 <li> FIXED: handle correctly flatten([_,[_]],L).</li>