use the right key for compressor configuration dump

The generated dump output is incorrect in sofar as it uses the name as
the key for this compressor, but they don't need to be equal as is the
case if you force some of the inbuilt ones to be disabled as our testing
framework does it at times.

This is hidden from changelog as nobody will actually notice while
describing it in a few words make it sound like an important change…

Git-Dch: Ignore

cmdline/apt-config.cc

@@ -29,6 +29,7 @@
 #include <iostream>
 #include <string>
 #include <vector>
+#include <map>
 #include <string.h>
 
 #include <apt-private/private-cmndline.h>
@@ -111,12 +112,19 @@ int main(int argc,const char *argv[])					/*{{{*/
    for (std::vector<std::string>::const_iterator a = archs.begin(); a != archs.end(); ++a)
       _config->Set("APT::Architectures::", *a);
 
+   string const conf = "APT::Compressor::";
+   std::map<std::string,std::string> CompressorNames;
+   for (auto && key : _config->FindVector("APT::Compressor", "", true))
+   {
+      auto const comp = conf + key + "::Name";
+      CompressorNames.emplace(_config->Find(comp, key), key);
+   }
    std::vector<APT::Configuration::Compressor> const compressors = APT::Configuration::getCompressors();
    _config->Clear("APT::Compressor");
-   string conf = "APT::Compressor::";
    for (std::vector<APT::Configuration::Compressor>::const_iterator c = compressors.begin(); c != compressors.end(); ++c)
    {
-      string comp = conf + c->Name + "::";
+      auto const n = CompressorNames.find(c->Name);
+      string comp = conf + (n == CompressorNames.end() ? c->Name : n->second) + "::";
       _config->Set(comp + "Name", c->Name);
       _config->Set(comp + "Extension", c->Extension);
       _config->Set(comp + "Binary", c->Binary);