Support to disable background compactions on a database.

Summary:
This option is needed for fast bulk uploads. The goal is to load
all the data into files in L0 without any interference from
background compactions.

Test Plan: make clean check

Reviewers: sheki

Reviewed By: sheki

CC: leveldb

Differential Revision: https://reviews.facebook.net/D6849

util/options.cc

@@ -51,7 +51,8 @@ Options::Options()
       no_block_cache(false),
       table_cache_numshardbits(4),
       compaction_filter_args(NULL),
-      CompactionFilter(NULL) {
+      CompactionFilter(NULL),
+      disable_auto_compactions(false) {
 }
 
 void
@@ -134,6 +135,8 @@ Options::Dump(
         compaction_filter_args);
     Log(log,"                       Options.CompactionFilter: %p",
         CompactionFilter);
+    Log(log,"               Options.disable_auto_compactions: %d",
+        disable_auto_compactions);
 }   // Options::Dump
 
 }  // namespace leveldb