+ httpx: allow custom Content-Disposition headers
! http: make multipart form-data more flexible but have it adhere to the RFC more strictly
merge with master

Conflicts:
	examples/spray-can/simple-http-server/src/main/scala/spray/examples/FileUploadHandler.scala
	spray-httpx/src/main/scala/spray/httpx/unmarshalling/MultipartUnmarshallers.scala
	spray-httpx/src/test/scala/spray/httpx/unmarshalling/FormDataUnmarshallersSpec.scala
! http(x): rename BodyPart.getName -> BodyPart.name, add BodyPart.dispositionParameterValue
+ httpx: add possibility to create a non-strict FormDataUnmarshaller
+ http: add simple access to BodyPart.filename / disposition
Merge pull request #536 from jrudolph/w/finish-pr-486

Completion of PR 486