fail the gradle build if git-hooks don't exist

check_for_git_hooks.gradle

// Apply by adding the following line to your build.gradle:
//    apply from: 'scripts/check_for_git_hooks.gradle'
// Comment out any hook files that aren't relevant for you.
final GIT_HOOK_DIR = ".git/hooks/"
final IGNORE_HOOKS_FLAG = "ignoreMissingHooks"
final GIT_HOOK_FILES = [
        "applypatch-msg",
        "commit-msg",
        "post-applypatch",
        "post-checkout",
        "post-commit",
        "post-merge",
        "post-receive",
        "post-rewrite",
        "post-update",
        "pre-applypatch",
        "pre-auto-gc",
        "pre-commit",
        "pre-push",
        "pre-rebase",
        "pre-receive",
        "prepare-commit-msg",
        "update"
]

def missing_hooks = GIT_HOOK_FILES.findAll { !(new File(GIT_HOOK_DIR + it).exists()) }
def ignore_missing_hooks = project.hasProperty(IGNORE_HOOKS_FLAG);
if (!missing_hooks.empty && !ignore_missing_hooks) {
    throw new IllegalStateException(
            "Git hooks not installed correctly! Missing these hooks: " + missing_hooks.join(", ")
                    + "\nadd -P$IGNORE_HOOKS_FLAG to skip this check")
}