WIP.  ledger-sort-region still drops the first transaction in the region.
Merge branch 'next' into ledger-mode-sort-region
Add regional sort facility to ledger mode

C-c C-s now bound to ledger-sort-region.  ledger-sort-region is smart and
find the beginning of the first xact within the region and the beginning of
the first xact AFTER the region so that it can keep posing structure intact