Fix %$ismember %rename predicate for members added via %extend

Bug reported was incorrect renaming of PHP built-in functions, such as
next. See PHPFN in phpkw.swg.

Add some tests for the %rename predicates.
guile std_string test: run test in utf8 locale

Guile can't properly handle non-ascii strings in the default C locale
Add %$isextendmember for %rename of members added via %extend
Merge branch 'master' of github.com:gjanssens/swig into gjanssens-master

* 'master' of github.com:gjanssens/swig:
  guile std_string test: run test in utf8 locale
  fix typo