hledger and hledger-web were reading their version number (and program
name) from their cabal files at compile time using cabal-file-th,
which allowed the version number be maintained in one place (per
package).
This meant you had to be in same directory as the cabal file when
building, which made life more complicated, eg emacs compilation mode
could not jump to errors. Also, it slowed down building slightly, and
is a factor in hledger Debian packages being unavailable on a number
of platforms (we also use TH for report templates).
Now, the build version is set with a CPP VERSION flag, which seems
simpler overall. For cabal builds, this needs to be configured
manually in a few more places in each cabal file. For makefile builds,
it is set it to the name of the most recent darcs tag (which should be
more useful than the old behaviour). If not set, it defaults to the
blank string, useful eg for haddock. And, all makefile builds now run
from the top directory.
