Make all the parameter names and options case sensitive

Make all the parameter names and options case sensitive

Changes "strcasecmp" to "strcmp".
This mainly deals with constant configuration options (e.g., enumerative
options and boolean options). For directive names, it's already
consistent (case sensitive), the parser functions are auto-generated.

The case sensitivity of the following parameter values is not changed:

- user and group names
- host names
- domain and realm names
- ACL names
- filesystem names
- options in request/response/digest messages