Git 1.6.4.4 on Windows with msysGit

Fixes since v1.6.4.3 -------------------- * The workaround for Github server that sometimes gave 500 (Internal server error) response to HEAD requests in 1.6.4.3 introduced a regression that caused re-fetching projects over http to segfault in certain cases due to uninitialized pointer being freed. * "git pull" on an unborn branch used to consider anything in the work tree and the index discardable. * "git diff -b/w" did not work well on the incomplete line at the end of the file, due to an incorrect hashing of lines in the low-level xdiff routines. * "git checkout-index --prefix=$somewhere" used to work when $somewhere is a symbolic link to a directory elsewhere, but v1.6.4.2 broke it. * "git unpack-objects --strict", invoked when receive.fsckobjects configuration is set in the receiving repository of "git push", did not properly check the objects, especially the submodule links, it received.