bug#13081: 24.3.50; doc of `compare-strings' says nothing about the compare function used

[Drew Adams]

1. I should have said that the doc problem applies to both the doc string and
Elisp manual.

2. What's more, the doc string says that "END1 and END2 default to".  This
language is incorrect - there is no defaulting.  These parameters are mandatory,
so they do not have any default values.

What the doc should say is two things:

a. START1, START2, END1, and END2 are either 0-based indexes into the string.
(This information is missing.)

b. START1, START2, END1, and END2 can each alternatively be nil.  For START1 and
START2, nil is the same as 0.  For END1 and END2, nil is the same as the length
of STR1 and STR2, respectively.