Build with locale support is broken  #101

This is https://sourceforge.net/p/aide/bugs/98

Hello.

Build with locale support has several problems, which cause build failures.

1. LOCALEDIR definition is missing from all existing build-system files.
   It used to be in configure.ac, then was moved to Makefile.am, where it silently died in commit 08cc29a.

2. Many incorrect usages of _ macro, which produce 'error: initializer element is not constant'.
   They all occur in one place: src/compare_db.c in details_string[] array definition.
   These must be converted to N_ instead. Similar examples:
   http://oss.sgi.com/archives/xfs/2008-12/msg01682.html