Problem: It's not easy to build Vim on Windows with XPM support.
Solution: Include the required files, they are quite small. Update the
MSVC makefile to use them. Binary files are in the next patch.
Problem: Memfile is not tested sufficiently. Looking up blocks in a
memfile is slow when there are many blocks.
Solution: Add high level test and unittest. Adjust the number of hash
buckets to the number of blocks. (Ivan Krasilnikov)