Make template and variable substitutions case insensitive

[pramsey]

In discussing ticket #3250, Steve said:

I was kinda wondering the same thing too, but even broader. The substitution code from mapstring.c is used primarily in 3 places:

• the runtime subs
• templates subs
• logical expression subs

There's already a case insensitive version of msReplaceSubstring() available in mapstring.c (as msCaseReplaceSubstring()). I don't know why we don't use that instead of the case sensitive version everywhere- unless there are big performance penalties. I wouldn't think that would break apps.

This isn't a RFC-able enhancement although running the msCaseReplaceSubstring() for msReplaceSubstring() by mapserver-devs would be a good idea.

[pramsey]

case insensitive template handling