Bug 11661: sanitize file names supplied to edithelp.pl

Bug 11661: sanitize file names supplied to edithelp.pl

This patch corrects an issue whereby edithelp.pl could
be used to create or modify arbitrary files on the server
with the permissions of the Apache user.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 7baf02c263a627b1454577b3141a0af4b8f963d1)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>