C++; added alternate property retrieval for signals and devices.
Remove 'ccache' from CXX variable before calling python build system.

Otherwise if CXX="ccache g++", then Python tries to build with just
"ccache" for some reason, and breaks.
Add a check for C++11 compiler flags.

Necessary since C++ headers use some C++11 features.
(Copied from liblo's configure.ac)
Make variable liblo_CXXFLAGS doesn't exist, pkg-config only supports CFLAGS.
Add some missing C++ headers in mapper_cpp.h.
Add 'const' qualifier to get() methods, allowing use of C++11 for-iterators.
C++: pass device or signal parent to property object and overload assignment operator.
Merge remote-tracking branch 'steve/master'
C++: Fixed ptr bug
C++: use set() function instead of wonky assignment operator overloading; rearranged class structure to match C API.
Test for forbidden keys in msig_set_property() and mdev_set_property().
Swig/Python: return timetag from start_queue() function.
Do not check for expired devices on every call to monitor_poll().
Use link pinging for estimating clock offsets, network latency and jitter between peers instead of admin-bus /sync messages. Simplify outgoing /sync messages but still accept old version.
Improvements to link sync.
C++: Fixed problems handling property values that are arrays/vectors of strings.
Switched properties named 'n_<something>' to 'num_<something>' for consistency.
Copy device name to signal props structure when signals are added after device registration.
Merge branch 'master' into output-vector-indexing