Merge branch 'cm/gitweb-project-list-persistent-cgi-fix' into maint

"gitweb" forgot to clear a global variable $search_regexp upon each
request, mistakenly carrying over the previous search to a new one
when used as a persistent CGI.

* cm/gitweb-project-list-persistent-cgi-fix:
  gitweb: fix problem causing erroneous project list