Fix new* and do* ebuild helpers to generate consistent error messages for

Fix new* and do* ebuild helpers to generate consistent error messages for
missing files and generate an appropriate QA Notice when such an error is
detected in the build log. Thanks to Diego 'Flameeyes' Pettenò <flameeyes@g.o>
for the suggestion. (trunk r11916)

svn path=/main/branches/2.1.6/; revision=11917