Pass failure exception to callback and target.

[JakeWharton]

Closes #1548. Closes #617.

[dnkoutso]

🚢

[dann1609]

Hey I'm updating library using gradle but callback is not updating. Right now I have version 2.5.2 someone have the same problem?

[NightlyNexus]

@dann1609 This change is unreleased. You can use the 3.0.0 snapshots if you need it.

repositories {
  maven { url 'https://oss.sonatype.org/content/repositories/snapshots/' }
}
dependencies {
  compile 'com.squareup.picasso:picasso:3.0.0-SNAPSHOT'
}