Enable UAC transition from ApacheMonitor running as a vanilla user without priv

Enable UAC transition from ApacheMonitor running as a vanilla user without priv
into a copy runas administrator with permissions (closing the original monitor),
in response to any start/stop/restart request who's control permissions failed.
This happens to work on Win2000 and later, although it is actually needed in
Win2008 or Vista and later, where by default under UAC, the admin user actually
has no permissions to control services unless the app is run elevated.

We don't want to do this at start time, and assault the user with auth attempts
at login before they have even asked to use the features of the Monitor.  Once
we've made the transition, we'll leave the new monitor running elevated.  Some
branding with the "security" shield icon is actually recommended by the CUA, but
I'm neglecting this for the moment.

This patch drops the single instance mutex for a search of existing windows of
our window's class & title, which is localized to the current session and just fine
for the purpose of restricting multiple invocations.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@633607 13f79535-47bb-0310-9956-ffa450edef68