add a test for the bug 20445 that resurected

examples/bts/20445.mlw

+module A
+axiom G : true
+end
+
+module B
+goal G : false
+clone A with goal G
+end
\ No newline at end of file

examples/bts/20445/why3session.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE why3session PUBLIC "-//Why3//proof session v5//EN"
+"http://why3.lri.fr/why3session.dtd">
+<why3session shape_version="4">
+<prover id="0" name="CVC4" version="1.4" timelimit="1" steplimit="0" memlimit="1000"/>
+<prover id="1" name="Alt-Ergo" version="1.30" timelimit="5" steplimit="0" memlimit="1000"/>
+<prover id="2" name="Z3" version="4.5.0" timelimit="1" steplimit="0" memlimit="1000"/>
+<prover id="3" name="CVC4" version="1.5" timelimit="1" steplimit="0" memlimit="1000"/>
+<file name="../20445.mlw">
+<theory name="A" proved="true" sum="d41d8cd98f00b204e9800998ecf8427e">
+</theory>
+<theory name="B" sum="3e4e0db7222351ee8b39dde6ac341e91">
+ <goal name="G">
+ <proof prover="0"><result status="unknown" time="0.00"/></proof>
+ <proof prover="1" timelimit="1"><result status="unknown" time="0.00"/></proof>
+ <proof prover="2"><result status="unknown" time="0.02"/></proof>
+ <proof prover="3"><result status="unknown" time="0.00"/></proof>
+ </goal>
+ <goal name="G" proved="true">
+ <proof prover="0"><result status="valid" time="0.00"/></proof>
+ <proof prover="1"><result status="valid" time="0.00" steps="1"/></proof>
+ <proof prover="2"><result status="valid" time="0.01"/></proof>
+ <proof prover="3"><result status="valid" time="0.00"/></proof>
+ </goal>
+</theory>
+</file>
+</why3session>