Prevent including the wrong include file by accident

[t-b]

[...]

1. If we try to force include /usr/local/include before any Tango directories, nothing happens. See: https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html#Directory-Options

   If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored.

   I observe the same behavior on Clang 8 on ubuntu bionic.
   Maybe this is different on FreeBSD.

2. Still, event.h may appear in other (non-system) directories and if that's the case, we get compilation errors, like:

   In file included from /home/michal/Documents/cppTango/cppapi/server/eventsupplier.h:61:
   /home/michal/Documents/cppTango/cppapi/client/eventconsumer.h:316:2: error: unknown type name 'EventQueue'
           EventQueue                      *ev_queue;
           ^
   

Switching to including full paths will be painful as you said because we have different directory structure in source tree compared to what is installed.

We also cannot just change <event> to "event" because it is located in client/ directory but included from both client/ and server/ directories. In latter case, we will not find this file in current directory and we fall-back to usual lookup order.

If this is really a problem for FreeBSD i suggest to just rename this file to something more unique.

Originally posted by @mliszcz in #711 (comment)