Exception handling: Added option to disable exception

The option could be enabled be setting either the enviorment Variable
RTT_IGNORE_EXCEPTION or be setting the static variable
RTT::m_catch_exception to a positive value.

This make the life for developers much easier. Let the Exception Raise
so that the user could use gdb for backtracke analysis. Only for Debuggig
purposes.
Merge branch 'master' of git.gitorious.org:orocos-toolchain/rtt