squash! Win32: support long paths

Squash in this commit text:
Test the case is when the full pathname length of a dir is close
to 260 (MAX_PATH).
Bug report and an original reproducer by Andrey Rogozhnikov.

Signed-off-by: Stepan Kasal <kasal@ucw.cz>

The rest is for record only:

The fix is to reserve space for "\*" in dirent_opendir().

ROOT=C:/smiths/workspace/ATM-hourly/SLAVE/build-win7-32
SUB1=data/data/gui/html/common/jwe/node_modules/lodash.merge/node_modules
SUB2A=node_modules/lodash._createwrapper/node_modules
SUB2=lodash._basecreatecallback/node_modules/lodash.bind/$SUB2A
SUB3A=node_modules/lodash._basecreate/node_modules/lodash._isnative
SUB3=lodash._basecreatewrapper/$SUB3A

cd C:/
mkdir -p $ROOT
cd $ROOT
git init

mkdir -p $SUB1 $SUB2 $SUB3
echo {} >> $SUB3/package.json
mv ${SUB3%%/*} $SUB2
mv ${SUB2%%/*} $SUB1

cd $ROOT
git --version
git config core.longpaths yes
git clean -fdx

Signed-off-by: Stepan Kasal <kasal@ucw.cz>