Fixes for three problems in mod_include:

Fixes for three problems in mod_include:
  * The ctx->tag_length computation in find_end_sequence() was a bit
    broken in cases where there was a "false alarm" match on a partial
    "-->"
  * The ap_ssi_get_tag_and_value() function needs to avoid walking off
    the end of the string.  After debugging this some more, I ended up
    using Cliff's original patch.
  * Infinite loop in is_only_below()

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94284 13f79535-47bb-0310-9956-ffa450edef68