Don't limit Q/A check for bad shebangs with just bin, sbin, libexec
and www. Scripts (with possibly incorrect shebangs) may be located
anywhere in ${PREFIX}, including, for instance, lib/ (multimedia/lives):

Error: '/usr/bin/perl' is an invalid shebang you need USES=shebangfix for 'lib/lives/plugins/effects/rendered/colour_replace'

and ${DATADIR}/ (databases/cego):

Error: '/bin/bash' is an invalid shebang you need USES=shebangfix for 'share/cego/cgbackup'

There may be some more false positives, but broken scripts are much
more severe problem. There's also whitelist mechanism which lets
you ignore shebangs for certain kinds of files (like .pm) which may
be extended to fix FPs

Approved by: portmgr (swills)
Differential Revision: D8923