Briefly document whitespace handling in sort

[The Wanderer]

I was tripped up by the fact that it is not indicated anywhere in the
provided documentation that the character count of a field, for the '-k'
option, is counted from the beginning of the preceding whitespace. The
attached patch adds to the usage message a somewhat terse note
explaining the situation.

If there's anything wrong with or otherwise objectionable about this,
don't hesitate to let me know; I'll either fix it if I can or attempt to
explain why I don't think it's a problem.

--
      The Wanderer

Warning: Simply because I argue an issue does not mean I agree with any
side of it.

Secrecy is the beginning of tyranny.

Index: src/sort.c
===================================================================
RCS file: /cvsroot/coreutils/coreutils/src/sort.c,v
retrieving revision 1.328
diff -u -u -r1.328 sort.c
--- src/sort.c  7 Oct 2005 18:48:28 -0000       1.328
+++ src/sort.c  7 Dec 2005 18:23:37 -0000
@@ -331,9 +331,10 @@
       fputs (_("\
 \n\
 POS is F[.C][OPTS], where F is the field number and C the character position\n\
-in the field.  OPTS is one or more single-letter ordering options, which\n\
-override global ordering options for that key.  If no key is given, use the\n\
-entire line as the key.\n\
+in the field.  If neither the -t nor the -b option is in effect, the 
characters\n\
+in a field are counted from the beginning of the preceding whitespace.  OPTS 
is\n\
+one or more single-letter ordering options, which override global ordering\n\
+options for that key.  If no key is given, use the entire line as the key.\n\
 \n\
 SIZE may be followed by the following multiplicative suffixes:\n\
 "), stdout);