*) core: make ap_escape_quotes() work correctly on strings

*) core: make ap_escape_quotes() work correctly on strings
   with more than MAX_INT/2 characters, counting quotes double.
   Credit to <generalbugs@zippenhop.com> for finding this.

*) core: improved checks in ap_escape_quotes() for
   extra long strings (or resulting strings) that
   exceed ptrdiff_t ranges.

Merge r1899609, r1899905 from trunk.
Reviewed by: icing, rpluem, ylavic
Submitted by: icing, ylavic

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1901196 13f79535-47bb-0310-9956-ffa450edef68