Also, implemented missing unit tests for the Iface function which opens
v4 sockets in IfaceMgr.

Reviewed by Thomas Markwalder on Jabber.

The comment at the end of adding to AM_CXXFLAGS was making the total
line too long, and the automake tool was splitting the line. This meant
that the macro assignment had an escaped comment, which the BSD make
interprets differently to GNU make (the latter swallows the next line as
part of the comment, whereas the former doesn't).

When bind10 is run in verbose mode, as is indicated to the user by
certain error messages, do not redirect b10-msgq's STDOUT to /dev/null
so that the user can see the actual cause for startup failure.

No ChangeLog entry required.

When there is an error connecting to the message queue socket file
because it wasn't cleaned up properly, and we know the name of the
socket file, display its name as part of the error message.

No ChangeLog entry required.

 - ChangeLog clarified
 - Comments in option_definition.h corrected

Okayed on jabber.

Added consts where applicable and extended comments.

As per review, update the tests to ensure that the existing message
queue daemon still works even after we have had a failed attempt to
start a second copy of the daemon.

Also, fix getting requested option codes from ORO.

As per review, don't use self._session for the check to see if there is
an existing message queue running. Rather, use a localally scoped
variable that will get cleaned up when the function exits.

Yet another make issue introduced with trac3186.  Unit test data files
are now looked for in the appropriate directory and copied as part of dist
check.

trac3186 added the user_chk hook library which had a couple of
uses of EXPECT_EQ on stl containers. Gtest 1.5 does not like this.

After merging, distcheck revealed a few minor issues with logging
files and unit test data files. These were corrected.

 - config parsers updated
 - new unit-tests for vendor options written
 - libdhcp++ cleaned up
 - fixes in option_vendor.cc
 - comments added and cleaned up

Mostly minor cosmetics. Added logic to select callouts to
simply return if no subnets are configured.