Speed up Snappy uncompression, new Logger interface.

- Removed one copy of an uncompressed block contents changing
  the signature of Snappy_Uncompress() so it uncompresses into a
  flat array instead of a std::string.
        
  Speeds up readrandom ~10%.

- Instead of a combination of Env/WritableFile, we now have a
  Logger interface that can be easily overridden applications
  that want to supply their own logging.

- Separated out the gcc and Sun Studio parts of atomic_pointer.h
  so we can use 'asm', 'volatile' keywords for Sun Studio.




git-svn-id: https://leveldb.googlecode.com/svn/trunk@39 62dab493-f737-651d-591e-8d6aee1b9529

db/db_bench.cc

@@ -472,13 +472,14 @@ class Benchmark {
     std::string compressed;
     bool ok = port::Snappy_Compress(input.data(), input.size(), &compressed);
     int64_t bytes = 0;
-    std::string uncompressed;
+    char* uncompressed = new char[input.size()];
     while (ok && bytes < 1024 * 1048576) {  // Compress 1G
       ok =  port::Snappy_Uncompress(compressed.data(), compressed.size(),
-                                    &uncompressed);
-      bytes += uncompressed.size();
+                                    uncompressed);
+      bytes += input.size();
       FinishedSingleOp();
     }
+    delete[] uncompressed;
 
     if (!ok) {
       message_ = "(snappy failure)";