Bug #49: Include guards became standard-compliant.

Some include guards used a name pattern which is reserved for the implementation
of a C++ compiler. This detail was fixed by the deletion of leading underscores.

The used prefixes were also made consistent.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge pull request #55 from elfring/Fix_reserved_identifier_violations

Make include guards standard-compliant.