SimilarityRenameDetector: Only attempt to index large files once

SimilarityRenameDetector: Only attempt to index large files once

If a file fails to index the first time the loop encounters it, the
file is likely to fail to index again on the next row.  Rather than
wasting a huge amount of CPU to index it again and fail, remember
which destination files failed to index and skip over them on each
subsequent row.

Because this condition is very unlikely, avoid allocating the BitSet
until its actually needed.  This keeps the memory usage unaffected
for the common case.

Change-Id: I93509b28b61a9bba8f681a7b4df4c6127bca2a09
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>