Fix hook installation on Linux

Marks the shell scripts executable and sets nullglob so that the lack of
merge drivers doesn't cause shenanigans.

tools/hooks/install.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+shopt -s nullglob
 cd "$(dirname "$0")"
 for f in *.hook; do
 	echo Installing hook: ${f%.hook}