Loop Vectorizer - skipping "bitcast" before GEP

Vectorization of memory instruction (Load/Store) is possible when the pointer is coming from GEP. The GEP analysis allows to estimate the profit.
In some cases we have a "bitcast" between GEP and memory instruction.
I added code that skips the "bitcast".

http://reviews.llvm.org/D13886

llvm-svn: 251291