Revert use of protobuf's Gzip streams.

Unfortunately some Red Hat-based distributions lack the required header.
See https://bugzilla.redhat.com/show_bug.cgi?id=815587

This reverts commit 261a389a76.
This reverts commit b6736eb0a5.

src/network/compressor.cc

@@ -0,0 +1,32 @@
+#include <zlib.h>
+
+#include "compressor.h"
+#include "dos_assert.h"
+
+using namespace Network;
+using namespace std;
+
+string Compressor::compress_str( const string &input )
+{
+  long unsigned int len = BUFFER_SIZE;
+  dos_assert( Z_OK == compress( buffer, &len,
+				reinterpret_cast<const unsigned char *>( input.data() ),
+				input.size() ) );
+  return string( reinterpret_cast<char *>( buffer ), len );
+}
+
+string Compressor::uncompress_str( const string &input )
+{
+  long unsigned int len = BUFFER_SIZE;
+  dos_assert( Z_OK == uncompress( buffer, &len,
+				  reinterpret_cast<const unsigned char *>( input.data() ),
+				  input.size() ) );
+  return string( reinterpret_cast<char *>( buffer ), len );
+}
+
+/* construct on first use */
+Compressor & Network::get_compressor( void )
+{
+  static Compressor the_compressor;
+  return the_compressor;
+}