Speed up N-gram counts when running extractor.

By replacing std::map with boost::unordered_map.

Runtime of extractor on 100-best lists of 2679 sentences:

Before:
real    0m35.314s
user    0m34.030s
sys     0m1.280s

Ater:
real    0m26.729s
user    0m25.420s
sys     0m1.310s

1 files changed, 1 insertions, 0 deletions

diff --git a/mert/BleuScorer.cpp b/mert/BleuScorer.cpp
index ba662680c..a3ba16b13 100644
--- a/mert/BleuScorer.cpp
+++ b/mert/BleuScorer.cpp
@@ -62,6 +62,7 @@ size_t BleuScorer::CountNgrams(const string& line, NgramCounts& counts,
     }
     for (size_t i = 0; i < encoded_tokens.size()-k+1; ++i) {
       vector<int> ngram;
+      ngram.reserve(encoded_tokens.size());
       for (size_t j = i; j < i+k && j < encoded_tokens.size(); ++j) {
         ngram.push_back(encoded_tokens[j]);
       }