Backport r1564727: Fix support for uploading files by using pushlstring...

Backport r1564727: Fix support for uploading files by using pushlstring instead of pushstring when pushing binary data.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1564729 13f79535-47bb-0310-9956-ffa450edef68