- add functions to set, get and generate a content-id for a mime part   . setContentId($id)   . getContentId()   . generateContentId()
- add functions to set, get and generate a content-id for a mime part
  . setContentId($id)
  . getContentId()
  . generateContentId()

- also, do not intermix boundary and content-type information but store
  them separately. If a boundary is set, add it to the content-type header
  on header creation.


git-svn-id: 526f3b90ad6d9b1dfe840af828070ca3d99521ac@2574 d2cacbed-c0f6-0310-851a-9dad52fc623a

johannes85/core