[perl #99382] 'stat' call documentation is poorly worded

The use of "block" to describe both the file-or-device-specific sweet
spot for I/O operations and the number of file-system-specific chunks
(not necessarily 512-byte chunks) is unfortunate.  I think we came by
it honestly because Perl just provides a wrapper around:

http://pubs.opengroup.org/onlinepubs/009695399/basedefs/sys/stat.h.html

which says:

blksize_t st_blksize A file system-specific preferred I/O block size for
                     this object. In some file system types, this may
                     vary from file to file.
blkcnt_t  st_blocks  Number of blocks allocated for this object.

and in the "Rationale" section they say:

"The unit for the st_blocks member of the stat structure is not
defined within IEEE Std 1003.1-2001. In some implementations it is 512
bytes. It may differ on a file system basis. There is no correlation
between values of the st_blocks and st_blksize, and the f_bsize (from
<sys/statvfs.h>) structure members."

The existing piece in perlfunc.pod was written in 1997 for Perl 5.003.
 Screens were smaller then.  Perhaps we could afford to wrap to a
second line now and say something like:

1 files changed, 4 insertions, 2 deletions

diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 08743ed499..5a2eb71da0 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -7401,8 +7401,10 @@ meanings of the fields:
   8 atime    last access time in seconds since the epoch
   9 mtime    last modify time in seconds since the epoch
  10 ctime    inode change time in seconds since the epoch (*)
- 11 blksize  preferred block size for file system I/O
- 12 blocks   actual number of blocks allocated
+ 11 blksize  preferred I/O size in bytes for interacting with the
+             file (may vary from file to file)
+ 12 blocks   actual number of system-specific blocks allocated
+             on disk (often, but not always, 512 bytes each)
 
 (The epoch was at 00:00 January 1, 1970 GMT.)