ruby: fix chaining calls to ContainerType#<<

Doing

  vector << 0 << 1

was resulting in a single-element vector (!)
ruby: fix ContainerType::StdVector#raw_memcpy

The method was looking at the vector type instead of the element type
to decide whether the memcpy was allowed at all.
ruby: validate the provided size in ContainerType::StdVector#raw_memcpy
ruby: fix documentation of ContainerType::StdVector#raw_memcpy
ruby: improve error reporting of ContainerType::StdVector.raw_memcpy
test,ruby: #raw_memcpy is part of StdVector, not ContainerType, reorganize the tests
Merge pull request #22 from orocos-toolchain/fix_to_raw_mempcy

fix raw mempcy (fixes #21)