cabal installation

[Frederik Eaton]

It would be nice if cabal would unlink destination files before
installing over them, rather than just calling "copyFile". It appears
that when "copyFile" finds that a destination file already exists,
rather than removing it, it tries to open and truncate it, which leads
cabal to fail with the following error message when a new version of a
running program is installed:

*** Exception: bar: copyFile: resource busy (Text file busy)

The commonly-used 'install' command does not suffer from this bug.

Frederik