Minor changes to comments, etc. for improving documentation generation

* encoding.c, threads.c, include/libxml/HTMLparser.h,
  doc/libxml2-api.xml: Minor changes to comments, etc. for
  improving documentation generation
* doc/Makefile.am: further adjustment to auto-generation of
  win32/libxml2.def.src
diff --git a/doc/Makefile.am b/doc/Makefile.am
index cb7d4c9..b51354c 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -69,10 +69,10 @@
 	-gtkdoc-mkdb --module=libxml --source-dir=$(DOC_SOURCE_DIR) --output-format=xml --main-sgml-file=$(DOC_MAIN_XML_FILE)
 
 
-libxml2-api.xml: apibuild.py ../include/libxml/*.h
+libxml2-api.xml: apibuild.py ../include/libxml/*.h ../*.c
 	-(./apibuild.py)
 
-$(WIN32_DIR)/libxml2.def.src:
+$(WIN32_DIR)/libxml2.def.src: libxml2-api.xml
 	-@(if [ -x $(bindir)/xsltproc ] ; then \
 	  $(bindir)/xsltproc -o $(WIN32_DIR)/libxml2.def.src \
 	  --nonet $(WIN32_DIR)/defgen.xsl libxml2-api.xml ; fi )