Fix http://bugs.webkit.org/show_bug.cgi?id=16448 ([GTK] Celtic Kane JavaScript perfor...

Fix bugs.webkit.org/show_bug.cgi?id=16448 ([GTK] Celtic Kane JavaScript performance on Array test is slow relative to Mac).

Reviewed by Maciej Stachowiak.

* kjs/array_instance.cpp:
(KJS::compareByStringPairForQSort):
(KJS::ArrayInstance::sort): Convert JSValue's to strings once up front and then sort the
results.  This avoids calling toString twice per comparison, but requires a temporary buffer
so we only use this approach in cases where the array being sorted is not too large.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@28782 268f45cc-cd09-0410-ab3c-d52691b4dbfc