Pipe integration test: added pipe files to the git ignore list.
Rx pipe: fixed a bug where the frame size was not properly checked.

The threaded function always waited for the buffer to be 1 byte larger than
the actual data frame size.
Pipe integration test: the test now works in a start/stop mode.

A start character is sent, the program sleeps, then sends a stop character.
This emulates the behaviour of the final CWIS camera application.