fixed bug #101003 on attribute-sets value computation in the presence of

* libxslt/attributes.c libxslt/xsltInternals.h libxslt/imports.c
  libxslt/xslt.c: fixed bug #101003 on attribute-sets value
  computation in the presence of imports
* tests/docs/Makefile.am tests/docs/bug-102.xml
  tests/general/Makefile.am tests/general/bug-102*: added an
  example in the regression tests for this case
Daniel