Related to #563, when rendering a transaction, we reserve two more chars
of width so that amounts remain aligned when there are posting flags.
Affects hledger-ui's transaction screen, print, hledger-rewrite etc.
Using "hledgerdev" was a hack to help ensure that tests used a fresh
developer build by default. Now they specify "hledger" again, which fits
better with stack. It's up to the tester to make sure the desired
executable is first in PATH or specified with -w. (Note a couple of
tests currently don't obey -w and will always run "hledger", see addons.test).
