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Conflicts:
	src/bin/dhcp4/config_parser.cc
	src/bin/dhcp6/config_parser.cc

Conflicts:
	src/lib/dhcpsrv/Makefile.am

Addendum to ticket 2524 - the makefile omitted to make sure the
dhcpsrv_messages.mes file were in the distribution tarball

Using g++, on some systems a call to system() is tagged with the
"warn unused result" attribute.  As all warnings are promoted to
errors, all uses of system() must use the returned status code.

I thought that explicit type name made the code more readable, but maybe
that's not the case so I've removed it now.

It still needs to be specified in the other constructor.

The method can be called by boost::bind directly.

When passing an argument to boost::bind by value, it was copied
(obviously, since it allowed removal of const). Add the const and use a
pointer to avoid the copy of possibly large object.

GCC requires the method passed to boost::bind to be public (not sure if
it is a bug or required by standard, but this way it compiles and it
doesn't expose anything anyway, since the class definition is in .cc).