bignum should always reset pre_alloc_base and recover Heap space

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@158 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

changes4.3.html

@@ -16,6 +16,8 @@
 
 <h2>Yap-4.3.20:</h2>
 <ul>
+	<li>FIXED: always release stack after InitBigNum  (report from
+	Nicos Angelopoulos).</li>
 	<li>FIXED: random would not load in windows  (report from
 	Henrik Bostr<74>m).</li>
 	<li>FIXED: don't send warnings about repeated predicates from