War on #ifdef NSCORE

I was recently bitten (again) by having written a small test-module
that forgot to #define NSCORE in the build-process, causing it to
behave oddly. Removing the '#ifdef NSCORE' statements entirely from
the header-files and replaceing it with the (for our sake) equivalent
'#ifndef NSCGI' takes care of such issues once and for all.

Now modules no longer need to care about macros used only by Nagios'
build process. That's a Good Thing, even if I do say so myself.

Signed-off-by: Andreas Ericsson <ae@op5.se>