LUCY-206 Spell out perlapi function to_utf8_lower.
LUCY-206 Spell out perlapi function to_utf8_lower.

Perl 5.15.6 has broken to_utf8_lower() in a way which is hard to fix.  Use the
underlying function Perl__to_utf8_lower_flags() for that specific Perl
version.

For earlier Perls, use the fully qualified function Perl_to_utf8_lower().
This probably speeds us up a bit on threaded perls, since we pass aTHX_
instead of getting the implicit context (see perlguts).

git-svn-id: 0e6074679e66e8f1cc73dfc755b08bab367f805b@1227324 13f79535-47bb-0310-9956-ffa450edef68

rbevers/lucy,kidaa/lucy,apache/lucy,apache/lucy,apache/lucy,nwellnhof/lucy,rbevers/lucy,rectang/lucy,apache/lucy,rectang/lucy,kidaa/lucy,pombredanne/apache-lucy,rectang/lucy,nwellnhof/lucy,nwellnhof/lucy,kidaa/lucy,pombredanne/apache-lucy,rectang/lucy,kidaa/lucy,pombredanne/apache-lucy,kidaa/lucy,kidaa/lucy,kidaa/lucy,nwellnhof/lucy,apache/lucy,rbevers/lucy,nwellnhof/lucy,rectang/lucy,pombredanne/apache-lucy,rectang/lucy,pombredanne/apache-lucy,rbevers/lucy,pombredanne/apache-lucy,rbevers/lucy,rbevers/lucy,pombredanne/apache-lucy,nwellnhof/lucy,apache/lucy,kidaa/lucy,apache/lucy,rbevers/lucy,rectang/lucy,nwellnhof/lucy