Add a check for missing python_check_deps() function

[mgorny]

The any-r1 API requires using both python_gen_any_dep and declaring python_check_deps() at the same time. It would be useful if we could detect if people doing are one and not the other.

I suppose for the former, it would be sufficient to do a dumb match on $(python_gen_any_dep. Seems unlikely enough to occur unexpected.

For the latter, would be nice to actually check global functions but I suppose a dumb regexp python_check_deps\s*() would also help.

[radhermit]

While waiting for proper bash parsing, pkgcheck could use a custom bash pkg source that leverages the ebd from pkgcore and provides various bash features such as a global function list dump. In essence, it would work similar to how the PerlCheck does except it would communicate with a bash-based daemon.

I don't think it shouldn't be overly slow as long as we keep the native bash functionality to a minimum in addition to spawning multiple ebds for multiprocess scanning to make use of.

[radhermit]

It would probably be even better to include defined functions as part of extended metadata dumps under the current design, however, I think the related discussion for that kind of stalled/died a while ago.