run-parts: permit dot later in file name

See https://gist.github.com/andyshinn/3ae01fa13cb64c9d36e7#gistcomment-2044506

To test:

    mkdir /tmp/testrp
    printf "#!/bin/sh\necho test\n" > /tmp/testrp/test.sh
    chmod a+x /tmp/testrp/*
    busybox run-parts /tmp/testrp
    test
    mv /tmp/testrp/test.sh /tmp/testrp/.test.sh
    busybox run-parts /tmp/testrp
    # no output

function                                             old     new   delta
act                                                  190     200     +10

Signed-off-by: Ján Sáreník <jajomojo@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

debianutils/run_parts.c

@@ -113,13 +113,24 @@ enum {
 };
 
 /* Is this a valid filename (upper/lower alpha, digits,
- * underscores, and hyphens only?)
+ * underscores, hyphens, and non-leading dots only?)
  */
 static bool invalid_name(const char *c)
 {
 	c = bb_basename(c);
 
-	while (*c && (isalnum(*c) || *c == '_' || *c == '-'))
+	if (*c == '.')
+		return *c;
+
+	/* Debian run-parts 4.8.3, manpage:
+	 * "...the names must consist entirely of ASCII letters,
+	 * ASCII digits, ASCII underscores, and ASCII minus-hyphens.
+	 * However, the name must not begin with a period."
+	 * The last sentence is a giveaway that something is fishy
+	 * (why mention leading dot if dots are not allowed anyway?).
+	 * Yes, you guessed it right: in fact non-leading dots ARE allowed.
+	 */
+	while (isalnum(*c) || *c == '_' || *c == '-' || *c == '.')
 		c++;
 
 	return *c; /* TRUE (!0) if terminating NUL is not reached */