[iterator.operations, range.iter.op.distance] Reword "get to".

It was previously not explicitly stated that input iterators would
actually be incremented (which invalidates copies). The new wording is
more explicit about how the distance is measured, and in doing so
calls out more explicitly that input iterators are indeed incremented.

Author: tkoeppe

source/iterators.tex

@@ -2763,11 +2763,9 @@
 \pnum
 \effects
 If \tcode{InputIterator} meets the \oldconcept{RandomAccessIterator} requirements,
-returns \tcode{(last - first)}; otherwise, returns
-the number of increments needed to get from
-\tcode{first}
-to
-\tcode{last}.
+returns \tcode{(last - first)}; otherwise, increments
+\tcode{first} until \tcode{last} is reached and returns
+the number of increments.
 \end{itemdescr}
 
 \indexlibraryglobal{next}%
@@ -2952,10 +2950,9 @@
 \effects
 If \tcode{S} and \tcode{I} model \tcode{\libconcept{sized_sentinel_for}<S, I>},
 returns \tcode{(last - first)};
-otherwise, returns the number of increments needed to get from
-\tcode{first}
-to
-\tcode{last}.
+otherwise, increments
+\tcode{first} until \tcode{last} is reached and returns
+the number of increments.
 \end{itemdescr}
 
 \indexlibraryglobal{distance}%