Register2: Add more sanity checks when converting TreePaths from one to another.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23049 57a11ea4-9604-0410-9ed3-97b8803252fd
Minor code cleanup: Decrease verbosity of register2 that makes the debugging output unreadable.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23050 57a11ea4-9604-0410-9ed3-97b8803252fd