Fix suexec invocations from userdir - the ~ was not being prepended to the

Fix suexec invocations from userdir - the ~ was not being prepended to the
uid per our convention.  Therefore, bad things would happen (like we
wouldn't cd to the right directory).

Add a flag to the ap_unix_identity_t structure to indicate if we are in
a userdir - if so, prefix the ~.

(Modified by Justin, but Colm's patch pointed me in the right direction.)

PR: 7810
Submitted by:	Colm <colmmacc@redbrick.dcu.ie>
Reviewed by:	Justin Erenkrantz

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94791 13f79535-47bb-0310-9956-ffa450edef68