* libxml.h: Applied following patches from Robert Collins
  and make sure IN_LIBXML is defined when compiling it
-------
* include/libxml/xmlversion.h.in (LIBXML_DLL_IMPORT): Use on Cygwin
  as well as Visual C.
* parser.c (XML_DIR_SEP): Don't use '\\' for Cygwin.
* parserInternals.c (XML_DIR_SEP): Don't use '\\' for Cygwin.
* strio.c (PLATFORM_UNIX): Define for Cygwin.
* triodef.h (TRIO_PLATFORM_UNIX): Define for Cygwin.
* xmlIO.c (xmlFileOpen): Use unix behaviour for Cygwin.
  Use binary mode opens for Cygwin (xmlFileOpenW xmlParserGetDirectory
  xmlSysIDExists xmlNoNetExists).
* xmllint.c: Don't include winsock2.h for Cygwin.
Daniel