only output doc attribute if a documentation file is specified in project, fixes #922130
only output doc attribute if a documentation file is specified in project, fixes #922130

nant/nantcontrib,cgourlay/nantcontrib,rmboggs/nantcontrib,cgourlay/nantcontrib,nant/nantcontrib,cgourlay/nantcontrib,rmboggs/nantcontrib,dahmage/nantcontrib,nant/nantcontrib,dahmage/nantcontrib,rmboggs/nantcontrib,dahmage/nantcontrib