fixed a serious problem when substituing entities using the Reader, the

* parser.c xmlreader.c include/libxml/parser.h: fixed a serious
  problem when substituing entities using the Reader, the entities
  content might be freed and if rereferenced would crash
* Makefile.am test/* result/*: added a new test case and a new
  test operation for the reader with substitution of entities.
Daniel
diff --git a/result/dav18.rde b/result/dav18.rde
new file mode 100644
index 0000000..9de17af
--- /dev/null
+++ b/result/dav18.rde
@@ -0,0 +1,13 @@
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+1 14 #text 0 1 
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