mkfs.jffs2: creating dirs in /

[Mike Frysinger]

with older mtd-utils, creating a directory in the root worked fine.
with current git, the parent dir search algo breaks this.

for example, just take the current git tree, build it up, and then run:
$ ./mkfs.jffs2 -d . -D device_table.txt -o /dev/null
mkfs.jffs2: skipping device_table entry '/dev': no parent directory!
mkfs.jffs2: skipping device_table entry '/dev/mem': no parent directory!
...
doing `mkdir dev` first works around the issue, but where's the fun in that.

locally i just made the change to interpret_table_entry() where it
looks to see if the dir is "/" and if so, uses "root" rather than
calling find_filesystem_entry(), but i dont think that's the right
long term fix.  i pondered the find_filesystem_entry() function for a
while, but the closest i found was to delete the first if statement
and then tweak the fullname[len] ...
-mike