doing case normalization as we do the lookup, avoiding the need 
for explicit lowercasing. Also tweak splitPrefixAndLocalname 
to avoid needless copiesin the normal, :-less case.

Gives about a 10-15% speedup on my attach-less (display:none) 
parsing benchmark, and about 1.4x or so speedup on getAttribute & 
similar microbenchmarks.

svn path=/branches/KDE/4.2/kdelibs/; revision=939348