Problem with pre-receive hook if there is whitespace character in file/folder name

Hello,

This is a suggestion for a change in: "pre-receive-hooks/block_file_extensions.sh". When you try to push an blob object, which has whitespace in its name, the current loop will break. My suggestion is to transform:

```
for FILE in `git log -1 --name-only --pretty=format:'' $COMMIT`;
do
case $FILE in
*.zip|*.gz|*.tgz )
echo "Hello there! We have restricted committing that filetype. Please see Dave in IT to discuss alternatives."
exit 1
;;
esac
done
```

into:
```
while IFS= read -r FILE; do
case "$FILE" in
*.zip|*.gz|*.tgz )
echo "Hello there! We have restricted committing that filetype. Please see Dave in IT to discuss alternatives."
exit 1
esac
done <<< "$(git log -1 --name-only --pretty=format:'' $COMMIT)"
```

Start with pre-receive-hooks/block_file_extensions.sh and inspect how the current git log output is iterated. Reproduce the hook with a file or folder name containing whitespace, then verify that the restricted extensions are still rejected and whitespace-containing names are processed correctly.

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