[master] rename exists() to isReadable() to better represent the intent.

also use is_open() instead of != NULL (it's strange that the original code
did even compile, but in any case this one should be better in clarity and
possibly in portability).
okayed on jabber, should be minor enough, directly pushing.

src/lib/datasrc/tests/sqlite3_accessor_unittest.cc

@@ -364,20 +364,19 @@ public:
     }
 };
 
-bool exists(const char* filename) {
-    std::ifstream f(filename);
-    return (f != NULL);
+bool isReadable(const char* filename) {
+    return (std::ifstream(filename).is_open());
 }
 
 TEST_F(SQLite3Create, creationtest) {
-    ASSERT_FALSE(exists(SQLITE_NEW_DBFILE));
+    ASSERT_FALSE(isReadable(SQLITE_NEW_DBFILE));
     // Should simply be created
     SQLite3Accessor accessor(SQLITE_NEW_DBFILE, RRClass::IN());
-    ASSERT_TRUE(exists(SQLITE_NEW_DBFILE));
+    ASSERT_TRUE(isReadable(SQLITE_NEW_DBFILE));
 }
 
 TEST_F(SQLite3Create, emptytest) {
-    ASSERT_FALSE(exists(SQLITE_NEW_DBFILE));
+    ASSERT_FALSE(isReadable(SQLITE_NEW_DBFILE));
 
     // open one manualle
     sqlite3* db;
@@ -393,7 +392,7 @@ TEST_F(SQLite3Create, emptytest) {
 }
 
 TEST_F(SQLite3Create, lockedtest) {
-    ASSERT_FALSE(exists(SQLITE_NEW_DBFILE));
+    ASSERT_FALSE(isReadable(SQLITE_NEW_DBFILE));
 
     // open one manually
     sqlite3* db;