move a couple of special warnings for SysV sems and Posix sems out of the

performance tuning guide and into the common Mutex documentation; remove the
other (duplicate) information from that guide and instead point to the Mutex
directive

mpm_common: axe docs for old accept mutex directives

worker and prefork: axe links to old accept mutex directives, mention the use
of the accept mutex and how it can be configured

event: axe links to old mutex directives where were already N/A

mod_rewrite: axe old RewriteLock directive, mention use of the rewrite map
mutex for RewriteMap programs and how it can be configured

fix other miscellaneous LockFile or AcceptMutex references


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@883878 13f79535-47bb-0310-9956-ffa450edef68