Fix constants for OS X

OS X has SQLite3 installed by default in the location indicated in this pull request.

Author: johnmyleswhite

src/Sqlite_consts.jl

@@ -7,7 +7,7 @@ let
     @linux_only lib_choices = ["libsqlite3"]
     @windows_only WORD_SIZE == 64 && (lib_choices = [Pkg.dir() * "\\Sqlite\\lib\\sqlite3-64"])
     @windows_only WORD_SIZE != 64 && (lib_choices = [Pkg.dir() * "\\Sqlite\\lib\\sqlite3"])
-    @osx_only lib_choices = [Pkg.dir() * "/Sqlite/lib/libsqlite3"]
+    @osx_only lib_choices = ["/usr/lib/libsqlite3.dylib", Pkg.dir() * "/Sqlite/lib/libsqlite3"]
     for lib in lib_choices 
         try
             dlopen(lib)
@@ -314,4 +314,4 @@ const SQLITE_TESTCTRL_EXPLAIN_STMT =             19 #
 const SQLITE_TESTCTRL_LAST =                     19 #
 
 #Virtual Table Configuration Options
-const SQLITE_VTAB_CONSTRAINT_SUPPORT =  1 #
+const SQLITE_VTAB_CONSTRAINT_SUPPORT =  1 #