Make ./snappy_unittest pass without "srcdir" being defined.

Previously, snappy_unittests would read from an absolute path /testdata/..;
convert it to use a relative path instead.

Patch from Marc-Antonie Ruel.

R=maruel


git-svn-id: https://snappy.googlecode.com/svn/trunk@72 03e5f5b5-db94-4691-08a0-1a8bf15f6143

snappy-test.cc

@@ -50,7 +50,7 @@ string ReadTestDataFile(const string& base) {
                            &contents,
                            file::Defaults()).CheckSuccess();
   } else {
-    file::ReadFileToString("/testdata/" + base,
+    file::ReadFileToString("testdata/" + base,
                            &contents,
                            file::Defaults()).CheckSuccess();
   }