Fix StrictMode crashes by calling close on our DexFiles

[abscondment]

When we enable StictMode, sugar occasionally throws the following sort of error:

java.lang.Throwable: Explicit termination method 'close' not called
    at dalvik.system.CloseGuard.open(CloseGuard.java:184)
    at dalvik.system.DexFile.<init>(DexFile.java:82)
    at com.orm.util.ReflectionUtil.getAllClasses(ReflectionUtil.java:295)
    at com.orm.util.ReflectionUtil.getDomainClasses(ReflectionUtil.java:253)
    at com.orm.SchemaGenerator.createDatabase(SchemaGenerator.java:37)
    at com.orm.SugarDb.onCreate(SugarDb.java:26)
    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:251)
    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
    at com.orm.SugarDb.getDB(SugarDb.java:36)
    at com.orm.SugarRecord.find(SugarRecord.java:189)
    [snip]

This is because instances of DexFile need to be closed when they're no longer needed. This patch cleans up resources to fix the crashing case.

[coveralls]

Coverage increased (+0.12%) to 71.01% when pulling ff29934 on madrona-labs:fix-strictmode into a45dd1a on satyan:master.

[black-snow]

@satyan @whoshuu please merge this