Postmaster/Main.hs: minor cosmetic change
postmaster.cabal: remove dependency on haskell98 library

This change fixes build errors with more recent compilers, like GHC 7.4.x.
postmaster.cabal: add the URL for reporting bugs
postmaster.cabal: update the tested-with field
postmaster.cabal: tentatively bump version to 0.3
Postmaster/Base.hs: adapt code to modern versions of Prelude that no longer export 'catch'