As mentioned a month or two ago there were some implicit assumptions that

the values in content_type, handler, content_encoding, ... were lowercase.
I'm not referring to mod_negotiation here -- there were other cases where
strcmp() was being used.  But in addition, mod_negotiation could be
convinced to call str_tolower() on r->content_language(s), which could
possibly modify a "read-only" string... which wastes at least one memory
page per child.

Clean all that up by declaring that the content fields in request_rec
(and related fields elsewhere) must be lowercase, and must not be modified
in place.  Naturally I chose this because it's more efficient... rather
than going around needlessly pstrdup()ing and strcasecmp()ing everywhere.

There are a few other tweaks in here I couldn't resist, along the lines
of getting rid of unneeded pstrdup()s.  Plus a new function
set_string_slot_lower().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80482 13f79535-47bb-0310-9956-ffa450edef68