shred: change default number of overwrites from 25 to 3

* src/shred.c: The concensus is that a default of 3
passes is appropriate for current drive technologies.
* src/TODO: Reference Paul Eggert's suggestion
of enhancing shred to conform to DoD 5220 rules.

TODO

@@ -107,6 +107,9 @@ sort: Investigate better sorting algorithms; see Knuth vol. 3.
   5.3.1, who credits Lester Ford, Jr. and Selmer Johnson, American
   Mathematical Monthly 66 (1959), 387-389.
 
+shred: Update shred as described here to conform to DoD 5220 rules:
+http://lists.gnu.org/archive/html/bug-coreutils/2007-05/msg00075.html
+
 Remove suspicious uses of alloca (ones that may allocate more than
    about 4k)
 

src/shred.c

@@ -102,7 +102,7 @@
 #include "randread.h"
 
 /* Default number of times to overwrite.  */
-enum { DEFAULT_PASSES = 25 };
+enum { DEFAULT_PASSES = 3 };
 
 /* How many seconds to wait before checking whether to output another
    verbose output line.  */