since the template files in the nix store are read-only, they can't be
overwritten the second time the album is generated. using cp's '-f'
option works around this.
So this was suggested as [long ago as October, 2015](https://github.com/NixOS/nixpkgs/issues/10376#issuecomment-147734898).
Despite being fairly ignorant of the nix Python support, I decided
that I really wanted this; this change brings in what I believe are
the necessary components---I have, at least, successfully run `beet
replaygain` and `beet bpd`---but it may not do it in the best way; I'm
happy to consider input on that front.
I can at least state that all three changes are necessary---leave any
one of them out and gstreamer support doesn't work.
Fixes this:
$ gscriptor
Can't load '/nix/store/17w6hdwbli924v7d43xxxp66qhgqpc24-perl-Pango-1.227/lib/perl5/site_perl/5.22.2/x86_64-linux-thread-multi/auto/Pango/Pango.so' for module Pango: /nix/store/17w6hdwbli924v7d43xxxp66qhgqpc24-perl-Pango-1.227/lib/perl5/site_perl/5.22.2/x86_64-linux-thread-multi/auto/Pango/Pango.so: undefined symbol: cairo_font_type_to_sv at /nix/store/5z1wn7knhckr3a0asb8lzp99sdai09f2-perl-5.22.2/lib/perl5/5.22.2/x86_64-linux-thread-multi/DynaLoader.pm line 193.
at /nix/store/srdac7af3nz6fb74haa8l8ls9wd9pas0-perl-Gtk2-1.2498/lib/perl5/site_perl/5.22.2/x86_64-linux-thread-multi/Gtk2.pm line 31.
Compilation failed in require at /nix/store/srdac7af3nz6fb74haa8l8ls9wd9pas0-perl-Gtk2-1.2498/lib/perl5/site_perl/5.22.2/x86_64-linux-thread-multi/Gtk2.pm line 31.
BEGIN failed--compilation aborted at /nix/store/srdac7af3nz6fb74haa8l8ls9wd9pas0-perl-Gtk2-1.2498/lib/perl5/site_perl/5.22.2/x86_64-linux-thread-multi/Gtk2.pm line 31.
Compilation failed in require at /nix/store/sgy2xsyvmam09pl25x8gb507gyiz9ybn-pcsc-tools-1.4.25/bin/.gscriptor-wrapped line 28.
BEGIN failed--compilation aborted at /nix/store/sgy2xsyvmam09pl25x8gb507gyiz9ybn-pcsc-tools-1.4.25/bin/.gscriptor-wrapped line 28.
