include JsonLocation in more mapping exceptions
Avoid setting explName to true if name is null in POJOPropertyBuilder

This change enables backwards compatibility of Jackson 2.4.0 with
modules relying on the 2.3 API (e.g., jackson-module-scala 2.3.X).

Prior to this change, old versions of jackson-module-scala would
receive this exception, when running with Jacskon 2.4:
```
java.lang.IllegalArgumentException: Can not pass true for 'explName' if name is null/empty
    at com.fasterxml.jackson.databind.introspect.POJOPropertyBuilder$Linked.<init>(POJOPropertyBuilder.java:955)
```

Note that this behavior is effectively what jackson-module-scala does in 2.4.0:
https://github.com/FasterXML/jackson-module-scala/blob/master/src/main/scala/com/fasterxml/jackson/module/scala/introspect/ScalaPropertiesCollector.scala#L211
Merge pull request #473 from aarondav/scala

Avoid setting explName to true if name is null in POJOPropertyBuilder
Merge pull request #464 from q3aiml/location-in-more-errors

include JsonLocation in more mapping exceptions
...
Merge pull request #472 from pfumagalli/master

Process injections when @JsonCreator annotated constructor is used.
Minor tweaking of a contribution