Porting libxml2 on zOS encoding of code

First set of patches for zOS
- entities.c parser.c tree.c xmlschemas.c xmlschemastypes.c xpath.c xpointer.c:
  ask conversion of code to ISO Latin 1 to avoid having the compiler assume
  EBCDIC codepoint for characters.
- xmlmodule.c: make sure we have support for modules
- xmlIO.c: zOS path names are special avoid dsome of the expectstions from
  Unix/Windows