Change VERSION to include the __DATE__ when compiling from within Xcode.
When building using "make xcode" or "make osxpkg" VERSION already is defined
to the "real" version number set in configure.in.
- make target "xcode" now detects the release number stored in the
configure.in file and passes it to Xcode.
- new make target "xcode-clean" which removes all files generated by
"make xcode" and removes the Xcode build directory.
Alexander Barton