Merge r960233 from trunk:

mod_rewrite: Allow to set environment variables without
explicitely giving a value.

Before this patch using [ENV=VAR] instead of [ENV=VAR:VAL]
silently drops the flag (it is added to the list of vars to set,
but then never actually set).

Submitted by: rjung
Reviewed by: rjung, niq, rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@964741 13f79535-47bb-0310-9956-ffa450edef68