Patch #823259: Update spec file:

- skip building HTML documentation if it is not available.
- Removal of patches, which can't be referenced from a build
directly from the tar-file.
- Using the RPM tmp directory macro for the buildroot location.
- Ensuring that the clean directive doesn't accidentally
delete the users root directory or another directory.
- --enable-unicode=ucs4 in configure line.
Backported to 2.3.