Bug#739154: libfishsound1-dev must depend on libflac-dev

[j at mailb.org]

Package: libfishsound1-dev
Version: 1.0.0-1.1
Severity: important

libfishsound1-dev currently does not depend on libflac-dev,
while its a build dependency.
As a result `pkg-config --libs libfishsound` fails with:

Package flac was not found in the pkg-config search path.
...

Making libfishsound1-dev depend on libflac-dev fixes this.