mkdir: allow 'mkdir -p' with trailing '/'

Let's suppose that /usr/tmp exists and one wants /usr/tmp/a/b
If one runs "mkdir -p /usr/tmp/a/b/" (the '/' at the end is
important), then a "File exists" error comes up. Example:

$ rm -rf /usr/tmp/a
$ mkdir -p /usr/tmp/a/b/
/usr/tmp/a/b/: File exists

This breaks gcc47 installation when C++ is enabled, and this
isn't the behaviour of mkdir on NetBSD nor Linix.

This patch fixes the above issue by dropping the trailing '/'.

commands/mkdir/mkdir.c

@@ -231,6 +231,10 @@ char *fordir;
 int makedir(dirname)
 char *dirname;
 {
+  while (strlen(dirname) > 1 && dirname[strlen(dirname) - 1] == '/') {
+    dirname[strlen(dirname) - 1] = '\0'; /* trim trailing '/' */
+  }
+
   if (mkdir(dirname, DEFAULT_MODE)) {
 	if (!pflag) {
 		perror(dirname);