add syntax checker for xlf

Author: Grégoire Paris

docs/hooks/syntax-checker.md

@@ -1,7 +1,10 @@
 # Description
 
 Checks for syntax errors in files that have a checker, based on the file extension.
-For the moment, there only is a php checker, located at `hooks/syntaxchecker/php/check.sh`.
+For the moment, there is :
+
+- a php checker, located at `hooks/syntaxchecker/php.sh`;
+- an xliff checker, located at `hooks/syntaxchecker/xlf.sh`.
 
 This hook is language-agnostic.
 

template/hooks/syntaxchecker/xlf.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+type xmllint > /dev/null 2>&1
+if [ $? -eq 0 ]
+then
+	xmllint $FILE > /dev/null
+fi