Warn about icon filenames with leading characters.
Review Request #122941 - Created March 14, 2015 and submitted
Through a quirk of implementation, old-style icon filenames are accepted by the new-style ecm_install_icons function. It's too late to change it now, as that would break existing projects, but we can warn about it.
Tests pass. The test output log shows the warning for the appropriate file, and not for other files.