Put file src attribute in quotes to allow more paths

[qrilka]

Nix paths allow only limited set of characters thus for example paths with "@" of paths with non-latin characters give derivation with Nix fails to parse. Quoting resolves this problem.

[qrilka]

@peti I'm quite sorry but this looks to be an incorrect PR:

• putting valid path (according to Nix) into double quotes results in Nix interpreting src as an URL for an archive which ends in something like

  unpacking sources
  unpacking source archive ./ab
  do not know how to unpack source archive ./ab
  

• using tricks like ./. + "/path" when "path" includes invalid (according to Nix) characters results in an error like

  invalid character 'Ð' in name 'аб'
  

Do you need a PR to revert this one? And sorry once again for not testing it thoroughly.

[peti]

I'll revert the patch in #404.

[qrilka]

Great, thank you.
BTW do you know if there are any documented constraints that Nix sets on paths it could use?
Comments around the line triggering error in make-derivation.nix have link to NixOS/nix#1771 but I couldn't find anything explicit about my question in that issue.