Add some cygwin fixes.
Add some cygwin fixes.

* Makefile.in:
  - from cygwin: add -no-undefined to the library link line

* conftools/get-version.sh: (new file)
  - script to extract the version number from expat.h

* configure.in:
  (some from the cygwin patch)
  - update the prereq to 2.52 instead of just 2.50
  - update the AC_INIT line to 2.52 standards: include the package
    name, version (with a lot of gunk to get this), and where to send
    bugs)
  - update the output file generation to 2.52 standards

* make-release.sh:
  - update to use the new get-version.sh script

* lib/expat.h:
  - from cygwin: add a little define for CYGWIN

markpizz/expat,markpizz/expat,markpizz/expat