positive → nonnegative doc fixes

* doc/lispref/numbers.texi (Bitwise Operations)
(Math Functions):
* doc/lispref/strings.texi (Formatting Strings):
* src/editfns.c (Fformat):
Correct “positive” with “nonnegative” in some documentation.

doc/lispref/numbers.texi

@@ -853,7 +853,7 @@ reproducing the same pattern moved over.
 bits in @var{integer1} to the left @var{count} places, or to the right
 if @var{count} is negative, bringing zeros into the vacated bits.  If
 @var{count} is negative, @code{lsh} shifts zeros into the leftmost
-(most-significant) bit, producing a positive result even if
+(most-significant) bit, producing a nonnegative result even if
 @var{integer1} is negative.  Contrast this with @code{ash}, below.
 
 Here are two examples of @code{lsh}, shifting a pattern of bits one
@@ -1233,7 +1233,7 @@ returns a NaN.
 
 @defun expt x y
 This function returns @var{x} raised to power @var{y}.  If both
-arguments are integers and @var{y} is positive, the result is an
+arguments are integers and @var{y} is nonnegative, the result is an
 integer; in this case, overflow causes truncation, so watch out.
 If @var{x} is a finite negative number and @var{y} is a finite
 non-integer, @code{expt} returns a NaN.

doc/lispref/strings.texi

@@ -1015,11 +1015,11 @@ numbered or unnumbered format specifications but not both, except that
   After the @samp{%} and any field number, you can put certain
 @dfn{flag characters}.
 
-  The flag @samp{+} inserts a plus sign before a positive number, so
+  The flag @samp{+} inserts a plus sign before a nonnegative number, so
 that it always has a sign.  A space character as flag inserts a space
-before a positive number.  (Otherwise, positive numbers start with the
-first digit.)  These flags are useful for ensuring that positive
-numbers and negative numbers use the same number of columns.  They are
+before a nonnegative number.  (Otherwise, nonnegative numbers start with the
+first digit.)  These flags are useful for ensuring that nonnegative
+and negative numbers use the same number of columns.  They are
 ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if
 both flags are used, @samp{+} takes precedence.
 

src/editfns.c

@@ -4195,8 +4195,8 @@ Nth argument is substituted instead of the next one.  A format can
 contain either numbered or unnumbered %-sequences but not both, except
 that %% can be mixed with numbered %-sequences.
 
-The + flag character inserts a + before any positive number, while a
-space inserts a space before any positive number; these flags only
+The + flag character inserts a + before any nonnegative number, while a
+space inserts a space before any nonnegative number; these flags only
 affect %d, %e, %f, and %g sequences, and the + flag takes precedence.
 The - and 0 flags affect the width specifier, as described below.