number of recv system call by caching the data. Each endpoint has a buffer
(the size is an MCA parameter) that can be use as a cache. Before each receive
operation this buffer is added at the end of the iovec list. All data that are
not expected by the fragment will go in this cache. If the cache contain data
all subsequent receive will just memcpy the data into the BTL buffers.
The only drawback is that we will spin around the receive_handle until all the
cached data is readed by the PML layer. This limitation come from the fact that
the event library is unable to call us if there is no events on the socket.
Therefore we are unable to keep the data in the cache until the next loop
into the progress engine.
This commit was SVN r8398.
