added more tests to increase test coverage

Changed all exceptions to inherit from senf::Exception
Replaced all throwErrno() calls with throw SystemException()

Replace all 'throw SystemException(...)' commands with 'throwErrno(...)'
Add additional links to documentation header

PPI: Fix cloneSource unit-test packet construction
Scheduler: BUGFIX: uninitialized loop variable
Scheduler: BUGFIX: delay deletions in fdTable_ (can't change map while iterating over it)
Add global 'valgrind' target
Add 'valgrind.sup' suppressions file to suppress custom benign valgrind errors
Fix all unit-tests to run correcly under valgrind (mostly timing adjustments)

Socket/Protocols/INet: Add INet4Address documentation
Fix some missed INet4Address -> INet4SocketAddress renames
Fixed several std:string arguments to use std::string const &

* Allow empty FileHandle/SocketHandle etc instances
* Make ServerSocketHandle::listen depend on AddressingPolicy
* Replace all occurences of inet_ntoa with inet_ntop (thread safety)
* Fix handling of exceptions in ReadHelper/WriteHelper
* Fix Scheduler ERR/HUP semantics

Unified emacs Local Variables

Renaned directory satscons to senfscons