Mostly adding "const" to methods that don't change the class, but
also correcting a few other points that were raised.

This is akin to the DuidPtr and is a shared point to a Client ID.

As the address is th eprimary key of the table, there can only ever
be at most one lease in the database with a given address.  Additional
selection by subnet ID is not needed.

The test used to create template files in a testdata folder without write
permissions. That caused 'make distcheck' errors. This regression had
been introduced with the ticket #2479. Okayed on jabber.

cppcheck was complaining about what was effectively:
const int A = 6; const int B = A; std::string array[b];

Changing this to
const int B = 6; std::string array[b];

... works

This reflects the fact that at the moment, the data is stored in
memory and not in a backing file.

in docs. trivial. no review.

okayed on jabber.

with fixing Conflicts for:
	src/lib/dns/gen-rdatacode.py.in
	src/lib/dns/tests/rdata_txt_like_unittest.cc

When tree.find() results in SUBDOMAIN, the node_path's top contains the
previous node.  Calling previousNode() yet again will return its
further previous node.

This test currently fails with an assertion.

with fixing Conflicts for
	src/lib/dns/gen-rdatacode.py.in
	src/lib/dns/rdata.cc
	src/lib/dns/rrparamregistry-placeholder.cc
	src/lib/dns/tests/rdata_hinfo_unittest.cc
	src/lib/dns/tests/rdata_txt_like_unittest.cc

this is actually ensured by the C++ standard lib spec.

due to limitation of the current implementation it doesn't work right now,
so commented out; planning to create a ticket to fix the underlying issue.