Revert "extras/slaveactivity: fix potential segfault if no master activity is set"

This reverts commit e1559a65b19cca6a695f33f9c51a4268ac8c864b.
Revert "SlaveActivity"

This reverts commit ed1d5f3f35221c3cb412fb1f002e5a3ede34055b.
ExecutionEngine: forward incoming messages to a master ExecutionEngine if set

The master ExecutionEngine is set automatically if the engine runs in a SlaveActivity whose master activity also runs an ExecutionEngine.

Signed-off-by: Johannes Meyer <johannes@intermodalics.eu>
Merge pull request #60 from orocos-toolchain/fix-59

SlaveActivity without master ExecutionEngine (pull request)

Functionally, the old behavior remains, but we delegate the responsibility from SlaveActivity to ExecutionEngine. Please yell if this breaks your case, but we believe it doesn't. The fatal error in the slave's trigger() function really needed to go since a slave without a master is quite valid.