resize2fs: don't print minimum size if fs is not clean

resize2fs: don't print minimum size if fs is not clean

Right now, resize2fs -P on a dirty filesystem will give you a number;
however, it's probably wrong if the fs is not clean:

# resize2fs -P myimage.img
resize2fs 1.41.9 (22-Aug-2009)
Estimated minimum size of the filesystem: 75623

# e2fsck -fy myimage.img
e2fsck 1.41.9 (22-Aug-2009)
myimage.img: recovering journal
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information

myimage.img: ***** FILE SYSTEM WAS MODIFIED *****
myimage.img: 9530/53760 files (0.1% non-contiguous), 24737/98304 blocks

# resize2fs -P myimage.img
resize2fs 1.41.9 (22-Aug-2009)
Estimated minimum size of the filesystem: 32165

We should issue the same "Please run e2fsck ..." message for
-P as we do for an actual resize request.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>