Whitespace cleanup and indentation fixes
Fixed friend and forward declarations of exec_context_data
to call it a struct (and not a class, for exec_context_data is a struct really)
New exec() variant which gets id and src_key from existing exec_context.
New method in exec_context to retrieve src_key from underlying sph.
Merge pull request #141 from ijon/master

src_key manipulation in the exec_context. Also new session::exec() variant which takes exec_context