PREG_OFFSET_CAPTURE: Mention byte offset (fix #4543)

Author: vrana

reference/pcre/constants.xml

@@ -45,7 +45,7 @@
       (<type>int</type>)
      </entry>
      <entry>
-      If this flag is set, for every occurring match the appendant string
+      If this flag is set, for every occurring match the appendant byte
       offset will also be returned. Note that this changes the return
       values in an array where every element is an array consisting of the
       matched string at offset 0 and its string offset within subject at