src/installer/utils.py: sort entries before writing out RECORD file

[kanavin]

This helps build reproducibility by ensuring the RECORD file is the same regardless of the order of the input files.

[eli-schwartz]

Note that it is wiser to delete the RECORD file anyway since you do not want to indicate to pip that it knows how to uninstall projects it didn't install and which are tracked by a more comprehensive installation database.

(Plans for pip to respect an INSTALLER identity fell through, unfortunately.)

[rossburton]

@eli-schwartz I like that argument. Can you point at prior art in eg gentoo as a rationale for doing it distro-wide?

[rossburton]

(and if that's a generally accepted point of view, maybe installer should have an option to not write them for the case where we don't expect anything to remove the packages?)

[rossburton]

Either way though, reproducible files are good.