openni_pcd_recorder: Fix memory size calculation for 32-bit system with >4GB RAM.

Systems with e.g. a Linux PAE kernel can have more than 4GB RAM, which
means the size should always be calculated using 64-bit integers.  The
memory available for buffering, however, must be addressable by a
std::size_t.
openni_pcd_recorder: Use a more realistic buffer size.

One PointCloud in a buffer is larger than 640*480 bytes.
Use sizeof(pcl::PointXYZRGBA) as a better approximation.
openni_pcd_recorder: Fix a small typo.
openni_pcd_recorder: Add command-line support for device IDs (like in openni_viewer).