display dialog if LilyPond is not found, instead of throwing an error
allow setting output as attribut, let parse() not overwrite it
double escaping not needed
Merge branch 'master' of github.com:wbsoft/frescobaldi
globbing not needed when constructing a search path
be sure include mac icons in source dist
oops
Merge pull request #272 from dliessi/no-lilypond-dialog

display dialog if LilyPond is not found, instead of throwing an error