cleanup, creating a new legacy.c module, made sure make tests ran in

* Makefile.am: cleanup, creating a new legacy.c module,
  made sure make tests ran in reduced conditions
* SAX.c SAX2.c configure.in entities.c globals.c parser.c
  parserInternals.c tree.c valid.c xlink.c xmlIO.c xmlcatalog.c
  xmlmemory.c xpath.c xmlmemory.c include/libxml/xmlversion.h.in:
  increased the modularization, allow to configure out
  validation code and legacy code, added a configuration
  option --with-minimum compiling only the mandatory code
  which then shrink to 200KB.
Daniel

xmlIO.c

@@ -1794,7 +1794,9 @@ xmlOutputBufferCreateFilename(const char *URI,
     void *context = NULL;
     char *unescaped;
 
+#ifdef LIBXML_HTTP_ENABLED
     int is_http_uri = 0;	/*   Can't change if HTTP disabled  */
+#endif
 
     if (xmlOutputCallbackInitialized == 0)
 	xmlRegisterDefaultOutputCallbacks();