Auto fix env-script-interpreter

[jayvdb]

https://build.opensuse.org/request/show/701428 was rejected because it was missing a .changes, but relevant here is that it also installed scripts into /usr/bin which had the wrong hashbang.

Perhaps cpanspec can add a block which fixes the interpreter for any script in the buildroot's /usr/bin which has the standard but undesirable interpreter. Or perhaps, the perl build itself can be configured with the appropriate shebang to use whenever required.